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Lee M, Kim Y, Mo SH, Kim S, Eom K, Lee H. Optoelectronic Synapse Based on 2D Electron Gas in Stoichiometry-Controlled Oxide Heterostructures. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024; 20:e2309851. [PMID: 38214690 DOI: 10.1002/smll.202309851] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 12/17/2023] [Indexed: 01/13/2024]
Abstract
Emulating synaptic functionalities in optoelectronic devices is significant in developing artificial visual-perception systems and neuromorphic photonic computing. Persistent photoconductivity (PPC) in metal oxides provides a facile way to realize the optoelectronic synaptic devices, but the PPC performance is often limited due to the oxygen vacancy defects that release excess conduction electrons without external stimuli. Herein, a high-performance optoelectronic synapse based on the stoichiometry-controlled LaAlO3/SrTiO3 (LAO/STO) heterostructure is developed. By increasing La/Al ratio up to 1.057:1, the PPC is effectively enhanced but suppressed the background conductivity at the LAO/STO interface, achieving strong synaptic behaviors. The spectral noise analyses reveal that the synaptic behaviors are attributed to the cation-related point defects and their charge compensation mechanism near the LAO/STO interface. The short-term and long-term plasticity is demonstrated, including the paired-pulse facilitation, in the La-rich LAO/STO device upon exposure to UV light pulses. As proof of concepts, two essential synaptic functionalities, the pulse-number-dependent plasticity and the self-noise cancellation, are emulated using the 5 × 5 array of La-rich LAO/STO synapses. Beyond the typical oxygen deficiency control, the results show how harnessing the cation stoichiometry can be used to design oxide heterostructures for advanced optoelectronic synapses and neuromorphic applications.
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Affiliation(s)
- Minkyung Lee
- Department of Physics, Ajou University, Suwon, 16499, Republic of Korea
- Department of Energy Systems Research, Ajou University, Suwon, 16499, Republic of Korea
| | - Youngmin Kim
- Department of Physics, Ajou University, Suwon, 16499, Republic of Korea
- Department of Energy Systems Research, Ajou University, Suwon, 16499, Republic of Korea
| | - Sang Hyeon Mo
- Department of Physics, Ajou University, Suwon, 16499, Republic of Korea
| | - Sungkyu Kim
- Department of Nanotechnology and Advanced Materials Engineering, Sejong University, Seoul, 05006, Republic of Korea
| | - Kitae Eom
- Department of Electronic Engineering, Gachon University, Seongnam, 13120, Republic of Korea
| | - Hyungwoo Lee
- Department of Physics, Ajou University, Suwon, 16499, Republic of Korea
- Department of Energy Systems Research, Ajou University, Suwon, 16499, Republic of Korea
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Rubano A, Paparo D. Optical Second Harmonic Generation on LaAlO 3/SrTiO 3 Interfaces: A Review. MATERIALS (BASEL, SWITZERLAND) 2023; 16:4337. [PMID: 37374522 DOI: 10.3390/ma16124337] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Revised: 05/30/2023] [Accepted: 05/31/2023] [Indexed: 06/29/2023]
Abstract
As we approach the limits of semiconductor technology, the development of new materials and technologies for the new era in electronics is compelling. Among others, perovskite oxide hetero-structures are anticipated to be the best candidates. As in the case of semiconductors, the interface between two given materials can have, and often has, very different properties, compared to the corresponding bulk compounds. Perovskite oxides show spectacular interfacial properties due to the the rearrangement of charges, spins, orbitals and the lattice structure itself, at the interface. Lanthanum aluminate and Strontium titanate hetero-structures (LaAlO3/SrTiO3) can be regarded as a prototype of this wider class of interfaces. Both bulk compounds are plain and (relatively) simple wide-bandgap insulators. Despite this, a conductive two-dimensional electron gas (2DEG) is formed right at the interface when a LaAlO3 thickness of n≥4 unit cells is deposited on a SrTiO3 substrate. The 2DEG is quite thin, being confined in only one or at least very few mono-layers at the interface, on the SrTiO3 side. A very intense and long-lasting study was triggered by this surprising discovery. Many questions regarding the origin and characteristics of the two-dimensional electron gas have been (partially) addressed, others are still open. In particular, this includes the interfacial electronic band structure, the transverse plane spatial homogeneity of the samples and the ultrafast dynamics of the confined carriers. Among a very long list of experimental techniques which have been exploited to study these types of interfaces (ARPES, XPS, AFM, PFM, …and many others), optical Second Harmonic Generation (SHG) was found to be suitable for investigating these types of buried interfaces, thanks to its extreme and selective interface-only sensitivity. The SHG technique has made its contribution to the research in this field in a variety of different and important aspects. In this work we will give a bird's eye view of the currently available research on this topic and try to sketch out its future perspectives.
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Affiliation(s)
- Andrea Rubano
- Physics Department "E. Pancini", University Federico II, Monte S. Angelo, Via Cintia, 80126 Naples, Italy
- Institute of Applied Sciences and Intelligent Systems (ISASI), Consiglio Nazionale delle Ricerche (CNR), Via Campi Flegrei 34, 80078 Pozzuoli, Italy
| | - Domenico Paparo
- Institute of Applied Sciences and Intelligent Systems (ISASI), Consiglio Nazionale delle Ricerche (CNR), Via Campi Flegrei 34, 80078 Pozzuoli, Italy
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Bhattacharya S, Datta S. Evidence of linear and cubic Rashba effect in non-magnetic heterostructure. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:205501. [PMID: 36848680 DOI: 10.1088/1361-648x/acbf94] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Accepted: 02/27/2023] [Indexed: 06/18/2023]
Abstract
TheLaAlO3/KTaO3system serves as a prototype to study the electronic properties that emerge as a result of spin-orbit coupling (SOC). In this article, we have used first-principles calculations to systematically study two types of defect-free (0 0 1) interfaces, which are termed as Type-I and Type-II. While the Type-I heterostructure produces a two dimensional (2D) electron gas, the Type-II heterostructure hosts an oxygen-rich 2D hole gas at the interface. Furthermore, in the presence of intrinsic SOC, we have found evidence of both cubic and linear Rashba interactions in the conduction bands of the Type-I heterostructure. On the contrary, there is spin-splitting of both the valence and the conduction bands in the Type-II interface, which are found to be only linear Rashba type. Interestingly, the Type-II interface also harbors a potential photocurrent transition path, making it an excellent platform to study the circularly polarized photogalvanic effect.
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Affiliation(s)
- Sanchari Bhattacharya
- Department of Physics and Astronomy, National Institute of Technology, Rourkela, 769008 Odisha, India
| | - Sanjoy Datta
- Department of Physics and Astronomy, National Institute of Technology, Rourkela, 769008 Odisha, India
- Center for Nanomaterials, National Institute of Technology, Rourkela, 769008 Odisha, India
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Yan X, Wrobel F, Tung IC, Zhou H, Hong H, Rodolakis F, Bhattacharya A, McChesney JL, Fong DD. Origin of the 2D Electron Gas at the SrTiO 3 Surface. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2200866. [PMID: 35429184 DOI: 10.1002/adma.202200866] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 04/04/2022] [Indexed: 06/14/2023]
Abstract
Bulk SrTiO3 is a well-known band insulator and the most common substrate used in the field of complex oxide heterostructures. Its surface and interface with other oxides, however, have demonstrated a variety of remarkable behaviors distinct from those expected. In this work, using a suite of in situ techniques to monitor both the atomic and electronic structures of the SrTiO3 (001) surface prior to and during growth, the disappearance and re-appearance of a 2D electron gas (2DEG) is observed after the completion of each SrO and TiO2 monolayer, respectively. The 2DEG is identified with the TiO2 double layer present at the initial SrTiO3 surface, which gives rise to a surface potential and mobile electrons due to vacancies within the TiO2-x adlayer. Much like the electronic reconstruction discovered in other systems, two atomic planes are required, here supplied by the double layer. The combined in situ scattering/spectroscopy findings resolve a number of longstanding issues associated with complex oxide interfaces, facilitating the employment of atomic-scale defect engineering in oxide electronics.
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Affiliation(s)
- Xi Yan
- Materials Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Friederike Wrobel
- Materials Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - I-Cheng Tung
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Hua Zhou
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Hawoong Hong
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Fanny Rodolakis
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Anand Bhattacharya
- Materials Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Jessica L McChesney
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Dillon D Fong
- Materials Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA
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Chen X, Zhang J, Liu B, Hu F, Shen B, Sun J. Two-dimensional conducting states in infinite-layer oxide/perovskite oxide hetero-structures. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 34:035003. [PMID: 34663765 DOI: 10.1088/1361-648x/ac30b6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 10/18/2021] [Indexed: 06/13/2023]
Abstract
Heterointerfaces sandwiched by oxides of dissimilar crystal structures will show strong interface reconstruction, leading to distinct interfacial effect arising from unusual physics. Here, we present a theoretical investigation on the interfaces between infinite-layer oxide and perovskite oxide (SrCuO2/SrTiO3and SrCuO2/KTaO3). Surprisingly, we found well-defined two-dimensional electron gas (2DEG), stemming from atomic reconstruction and polar discontinuity at interface. Moreover, the 2DEG resides in both the TiO2and CuO2interfacial layers, unlike LaAlO3/SrTiO3for which 2DEG exists only in the TiO2interfacial layer. More than that, no metal-to-insulator transition is observed as the SrCuO2layer thickness decreases to one unit cell, i.e., the metallicity of the new interface is robust. Further investigations show more unique features of the 2DEG. Due to the absence of apical oxygen at the SrCuO2/SrTiO3(KTaO3) interface, the conducting states in the interface TiO2(TaO2) layer follows thedxy<d3z2-r2<dxz/yzorbital order rather than thedxy<dxz/yzorbital order of paradigm LaAlO3/SrTiO3(KTaO3), exhibiting enhanced interfacial conduction. This work suggests the great potential of heterointerfaces composed of non-isostructural oxides for fundamental research.
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Affiliation(s)
- Xiaobing Chen
- Beijing National Laboratory for Condensed Matter Physics & Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Jine Zhang
- School of Integrated Circuit Science and Engineering, Beihang University, Beijing 100191, People's Republic of China
| | - Banggui Liu
- Beijing National Laboratory for Condensed Matter Physics & Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Fengxia Hu
- Beijing National Laboratory for Condensed Matter Physics & Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, People's Republic of China
| | - Baogen Shen
- Beijing National Laboratory for Condensed Matter Physics & Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, People's Republic of China
| | - Jirong Sun
- Beijing National Laboratory for Condensed Matter Physics & Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, People's Republic of China
- Spintronics Institute, University of Jinan, Jinan, Shandong 250022, People's Republic of China
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Leermakers I, Rubi K, Yang M, Kerdi B, Goiran M, Escoffier W, Rana AS, Smink AEM, Brinkman A, Hilgenkamp H, Maan JC, Zeitler U. Quantum oscillations in an optically-illuminated two-dimensional electron system at the LaAlO 3/SrTiO 3interface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:465002. [PMID: 34433152 DOI: 10.1088/1361-648x/ac211a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Accepted: 08/25/2021] [Indexed: 06/13/2023]
Abstract
We have investigated the illumination effect on the magnetotransport properties of a two-dimensional electron system at the LaAlO3/SrTiO3interface. The illumination significantly reduces the zero-field sheet resistance, eliminates the Kondo effect at low-temperature, and switches the negative magnetoresistance into the positive one. A large increase in the density of high-mobility carriers after illumination leads to quantum oscillations in the magnetoresistance originating from the Landau quantization. The carrier density (∼2 × 1012 cm-2) and effective mass (∼1.7me) estimated from the oscillations suggest that the high-mobility electrons occupy thedxz/yzsubbands of Ti:t2gorbital extending deep within the conducting sheet of SrTiO3. Our results demonstrate that the illumination which induces additional carriers at the interface can pave the way to control the Kondo-like scattering and study the quantum transport in the complex oxide heterostructures.
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Affiliation(s)
- I Leermakers
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - K Rubi
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - M Yang
- Laboratoire National des Champs Magnétiques Intenses (LNCMI-EMFL), Université de Toulouse, CNRS, INSA, UPS, 143 Avenue de Rangueil, 31400 Toulouse, France
| | - B Kerdi
- Laboratoire National des Champs Magnétiques Intenses (LNCMI-EMFL), Université de Toulouse, CNRS, INSA, UPS, 143 Avenue de Rangueil, 31400 Toulouse, France
| | - M Goiran
- Laboratoire National des Champs Magnétiques Intenses (LNCMI-EMFL), Université de Toulouse, CNRS, INSA, UPS, 143 Avenue de Rangueil, 31400 Toulouse, France
| | - W Escoffier
- Laboratoire National des Champs Magnétiques Intenses (LNCMI-EMFL), Université de Toulouse, CNRS, INSA, UPS, 143 Avenue de Rangueil, 31400 Toulouse, France
| | - A S Rana
- MESA + Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
| | - A E M Smink
- MESA + Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
| | - A Brinkman
- MESA + Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
| | - H Hilgenkamp
- MESA + Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
| | - J C Maan
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
| | - U Zeitler
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands
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Song K, Min T, Seo J, Ryu S, Lee H, Wang Z, Choi S, Lee J, Eom C, Oh SH. Electronic and Structural Transitions of LaAlO 3 /SrTiO 3 Heterostructure Driven by Polar Field-Assisted Oxygen Vacancy Formation at the Surface. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2021; 8:e2002073. [PMID: 34029001 PMCID: PMC8292910 DOI: 10.1002/advs.202002073] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 02/22/2021] [Indexed: 05/16/2023]
Abstract
The origin of 2D electron gas (2DEG) at LaAlO3 /SrTiO3 (LAO/STO) interfaces has remained highly controversial since its discovery. Various models are proposed, which include electronic reconstruction via surface-to-interface charge transfer and defect-mediated doping involving cation intermixing or oxygen vacancy (VO ) formation. It is shown that the polar field-assisted VO formation at the LAO/STO surface plays critical roles in the 2DEG formation and concurrent structural transition. Comprehensive scanning transmission electron microscopy analyses, in conjunction with density functional theory calculations, demonstrate that VO forming at the LAO/STO surface above the critical thickness (tc ) cancels the polar field by doping the interface with 2DEG. The antiferrodistortive (AFD) octahedral rotations in LAO, which are suppressed below the tc , evolve with the formation of VO above the tc . The present study reveals that local symmetry breaking and shallow donor behavior of VO induce the AFD rotations and relieve the electrical field by electron doping the oxide heterointerface.
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Affiliation(s)
- Kyung Song
- Materials Testing and Reliability DivisionKorea Institute of Materials Science (KIMS)Changwon51508Republic of Korea
- Department of Materials Science and EngineeringPohang University of Science and Technology (POSTECH)Pohang37673Republic of Korea
| | - Taewon Min
- Department of PhysicsPusan National UniversityBusan46241Republic of Korea
| | - Jinsol Seo
- Department of Energy ScienceSungkyunkwan UniversitySuwon16419Republic of Korea
| | - Sangwoo Ryu
- Department of Materials Science and EngineeringUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Hyungwoo Lee
- Department of Materials Science and EngineeringUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Zhipeng Wang
- Department of Energy ScienceSungkyunkwan UniversitySuwon16419Republic of Korea
| | - Si‐Young Choi
- Materials Testing and Reliability DivisionKorea Institute of Materials Science (KIMS)Changwon51508Republic of Korea
- Department of Materials Science and EngineeringPohang University of Science and Technology (POSTECH)Pohang37673Republic of Korea
| | - Jaekwang Lee
- Department of PhysicsPusan National UniversityBusan46241Republic of Korea
| | - Chang‐Beom Eom
- Department of Materials Science and EngineeringUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Sang Ho Oh
- Department of Materials Science and EngineeringPohang University of Science and Technology (POSTECH)Pohang37673Republic of Korea
- Department of Energy ScienceSungkyunkwan UniversitySuwon16419Republic of Korea
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Fang L, Chen C, Sundaresan A, Narayana C, Ter-Oganessian N, Pyatakov AP, Cao S, Zhang J, Ren W. The CdTiO 3/BaTiO 3 superlattice interface from first principles. NANOSCALE 2021; 13:8506-8513. [PMID: 33904555 DOI: 10.1039/d1nr00374g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The oxide interface has been studied extensively in the past decades and exhibits different physical properties from the constituent bulks. Using first-principles electronic structure calculations, we investigated the interface of CdTiO3/BaTiO3 (CTO/BTO) superlattice with ferroelectric BaTiO3. In this case, the conduction bands of CdTiO3 are composed of Cd-5s orbitals with low electron effective mass and nondegenerate dispersion, and thus expected to have high mobility. We predicted a controllable conductivity at the interface, and further analyzed how the polarization direction and strength affect the conductivity. We also explored the relationship between two components: thickness and polarization. Intriguingly, the total polarization in CTO/BTO might be even larger than that of ferroelectric bulk BaTiO3. Therefore, we found a way to maximize the superlattice polarization by increasing the fraction of the CdTiO3 layers, based on the interesting dependence of the total polarization and CTO/BTO ratio.
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Affiliation(s)
- Le Fang
- Materials Genome Institute, International Center for Quantum and Molecular Structures, Shanghai University, Shanghai 200444, China.
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Chen J, Zhang Z, Luo L, Lu Y, Song C, Cheng D, Chen X, Li W, Ren Z, Wang J, Tian H, Zhang Z, Han G. Reversible magnetism transition at ferroelectric oxide heterointerface. Sci Bull (Beijing) 2020; 65:2094-2099. [PMID: 36732962 DOI: 10.1016/j.scib.2020.09.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Revised: 08/11/2020] [Accepted: 09/01/2020] [Indexed: 02/04/2023]
Abstract
Oxide heterointerface is a platform to create unprecedented two-dimensional electron gas, superconductivity and ferromagnetism, arising from a polar discontinuity at the interface. In particular, the ability to tune these intriguing effects paves a way to elucidate their fundamental physics and to develop novel electronic/magnetic devices. In this work, we report for the first time that a ferroelectric polarization screening at SrTiO3/PbTiO3 interface is able to drive an electronic construction of Ti atom, giving rise to room-temperature ferromagnetism. Surprisingly, such ferromagnetism can be switched to antiferromagnetism by applying a magnetic field, which is reversible. A coupling of itinerant electrons with local moments at interfacial Ti 3d orbital was proposed to explain the magnetism. The localization of the itinerant electrons under a magnetic field is responsible for the suppression of magnetism. These findings provide new insights into interfacial magnetism and their control by magnetic field relevant interfacial electrons promising for device applications.
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Affiliation(s)
- Jialu Chen
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China
| | - Zijun Zhang
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China; Center of Electron Microscope, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
| | - Liang Luo
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory-USDOE, Ames, IA 50011, USA
| | - Yunhao Lu
- Department of Physics, Zhejiang University, Hangzhou 310027, China
| | - Cheng Song
- Key Laboratory of Advanced Materials (Ministry of Education), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
| | - Di Cheng
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory-USDOE, Ames, IA 50011, USA
| | - Xing Chen
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China; Center of Electron Microscope, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
| | - Wei Li
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China
| | - Zhaohui Ren
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China.
| | - Jigang Wang
- Department of Physics and Astronomy, Iowa State University and Ames Laboratory-USDOE, Ames, IA 50011, USA.
| | - He Tian
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China; Center of Electron Microscope, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China.
| | - Ze Zhang
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China; Center of Electron Microscope, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
| | - Gaorong Han
- State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Cyrus Tang Center for Sensor Materials and Application, Zhejiang University, Hangzhou 310027, China.
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The emergence of magnetic ordering at complex oxide interfaces tuned by defects. Nat Commun 2020; 11:3650. [PMID: 32686663 PMCID: PMC7371687 DOI: 10.1038/s41467-020-17377-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Accepted: 06/27/2020] [Indexed: 11/08/2022] Open
Abstract
Complex oxides show extreme sensitivity to structural distortions and defects, and the intricate balance of competing interactions which emerge at atomically defined interfaces may give rise to unexpected physics. In the interfaces of non-magnetic complex oxides, one of the most intriguing properties is the emergence of magnetism which is sensitive to chemical defects. Particularly, it is unclear which defects are responsible for the emergent magnetic interfaces. Here, we show direct and clear experimental evidence, supported by theoretical explanation, that the B-site cation stoichiometry is crucial for the creation and control of magnetism at the interface between non-magnetic ABO3-perovskite oxides, LaAlO3 and SrTiO3. We find that consecutive defect formation, driven by atomic charge compensation, establishes the formation of robust perpendicular magnetic moments at the interface. Our observations propose a route to tune these emerging magnetoelectric structures, which are strongly coupled at the polar-nonpolar complex oxide interfaces.
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Chen Y, Lechaux Y, Casals B, Guillet B, Minj A, Gázquez J, Méchin L, Herranz G. Photoinduced Persistent Electron Accumulation and Depletion in LaAlO_{3}/SrTiO_{3} Quantum Wells. PHYSICAL REVIEW LETTERS 2020; 124:246804. [PMID: 32639817 DOI: 10.1103/physrevlett.124.246804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 05/14/2020] [Indexed: 06/11/2023]
Abstract
Persistent photoconductance is a phenomenon found in many semiconductors, by which light induces long-lived excitations in electronic states. Commonly, persistent photoexcitation leads to an increase of carriers (accumulation), though occasionally it can be negative (depletion). Here, we present the quantum well at the LaAlO_{3}/SrTiO_{3} interface, where in addition to photoinduced accumulation, a secondary photoexcitation enables carrier depletion. The balance between both processes is wavelength dependent, and allows tunable accumulation or depletion in an asymmetric manner, depending on the relative arrival time of photons of different frequencies. We use Green's function formalism to describe this unconventional photoexcitation, which paves the way to an optical implementation of neurobiologically inspired spike-timing-dependent plasticity.
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Affiliation(s)
- Yu Chen
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Catalonia, Spain
| | - Yoann Lechaux
- Normandie Univ, UNICAEN, ENSICAEN, CNRS, GREYC, 14000 Caen, France
| | - Blai Casals
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Catalonia, Spain
| | - Bruno Guillet
- Normandie Univ, UNICAEN, ENSICAEN, CNRS, GREYC, 14000 Caen, France
| | - Albert Minj
- Normandie Univ, UNICAEN, ENSICAEN, CNRS, GREYC, 14000 Caen, France
- IMEC, Kapeldreef 75, Leuven 3000, Belgium
| | - Jaume Gázquez
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Catalonia, Spain
| | - Laurence Méchin
- Normandie Univ, UNICAEN, ENSICAEN, CNRS, GREYC, 14000 Caen, France
| | - Gervasi Herranz
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Catalonia, Spain
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12
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Wang Y, Zhao H, Wang C, Huo D, Su H, Ma X, Zhang J. Multi-frequency surface plasmons supported with a nanoscale non-uniform 2D electron gas formed due to a polar catastrophe at the oxide interface, dispersions, diffractions, and beyond. NANOSCALE 2020; 12:7082-7097. [PMID: 32191240 DOI: 10.1039/c9nr07634d] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Recently, 2D electron gases (2DEGs) formed at oxide interfaces are drawing increasing attention as they cause a myriad of intriguing phenomena. As ideal platforms in supporting surface plasmon polaritons (SPPs) without metallic constituents, such 2DEGs are favorable in non-linear plasmonics for ultra-low total Joule dissipation. Convincingly, an increase in the interfacial electron density (IIED) formed at the interface of indium-tin-oxide and LiNbO3 composite slab is responsible for a number of interesting phenomena, which are hardly explained with the conventional photorefractive theoretical framework but can be satisfactorily elucidated via SPP excitation and resultant colossal non-linear effects. Since the polar-catastrophe-led IIED is universal to all combinations of highly polar ferroelectric oxides (FOs) and less polar transparent conducting oxides (TCOs), a systematic theoretical treatment of an FO/TCO system is pivotal to a variety of promising applications. In this study, the nanometer scale 2DEG at the FO/TCO interface is illustrated theoretically with the Thomas-Fermi screening picture, by taking into account the spontaneous polarization, along with related boundary conditions. The local plasma frequency of 2DEGs can be increased up to the UV regime for the composite slabs discussed, which are suitable for highly desirable visible applications. The SPP dispersion relationship was given for the 2DEG layer sandwiched between the FO slab and the unmodified TCO layer. To further take the non-uniform nature of IIED into account, dramatic dispersions of dielectric permittivity and index of refraction were simulated with a very broad range, hinting at different ways for meeting phase matching conditions and slowing the light for non-linear plasmonic applications, which are confirmed experimentally.
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Affiliation(s)
- Yingce Wang
- Institute of Modern Optics, School of Physics, Harbin Institute of Technology, Harbin, 150001, China.
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13
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Mori R, Marshall PB, Ahadi K, Denlinger JD, Stemmer S, Lanzara A. Controlling a Van Hove singularity and Fermi surface topology at a complex oxide heterostructure interface. Nat Commun 2019; 10:5534. [PMID: 31797932 PMCID: PMC6892806 DOI: 10.1038/s41467-019-13046-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 10/16/2019] [Indexed: 11/10/2022] Open
Abstract
The emergence of saddle-point Van Hove singularities (VHSs) in the density of states, accompanied by a change in Fermi surface topology, Lifshitz transition, constitutes an ideal ground for the emergence of different electronic phenomena, such as superconductivity, pseudo-gap, magnetism, and density waves. However, in most materials the Fermi level, \documentclass[12pt]{minimal}
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\begin{document}$${E}_{{\rm{F}}}$$\end{document}EF, is too far from the VHS where the change of electronic topology takes place, making it difficult to reach with standard chemical doping or gating techniques. Here, we demonstrate that this scenario can be realized at the interface between a Mott insulator and a band insulator as a result of quantum confinement and correlation enhancement, and easily tuned by fine control of layer thickness and orbital occupancy. These results provide a tunable pathway for Fermi surface topology and VHS engineering of electronic phases. A singularity in a material’s density of states at the Fermi energy can drive the formation of unconventional electronic phases. Here the authors show a Van Hove singularity is tunable across the Fermi energy in an oxide heterostructure, leading to enhanced electronic correlations.
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Affiliation(s)
- Ryo Mori
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.,Applied Science & Technology, University of California, Berkeley, CA, 94720, USA
| | - Patrick B Marshall
- Materials Department, University of California, Santa Barbara, CA, 93106-5050, USA
| | - Kaveh Ahadi
- Materials Department, University of California, Santa Barbara, CA, 93106-5050, USA
| | - Jonathan D Denlinger
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Susanne Stemmer
- Materials Department, University of California, Santa Barbara, CA, 93106-5050, USA
| | - Alessandra Lanzara
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. .,Department of Physics, University of California, Berkeley, CA, 94720, USA.
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14
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Bhandari C, Satpathy S. Two dimensional electron gas in the [Formula: see text]-doped iridates with strong spin-orbit coupling: La[Formula: see text]Sr 2IrO 4. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:435505. [PMID: 31272089 DOI: 10.1088/1361-648x/ab2f3f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Iridates are of considerable current interest because of the strong spin-orbit coupling that leads to a variety of new phenomena. Using density-functional studies, we predict the formation of a spin-orbital entangled two dimensional electron gas (2DEG) in the [Formula: see text]-doped iridate La[Formula: see text]Sr2IrO4, where a single SrO layer is replaced by a LaO layer. The extra La electron resides close to the [Formula: see text]-doped layer, partially occupying the [Formula: see text] upper Hubbard band and thereby making the interface metallic. The magnetic structure of the bulk is destroyed near the interface, with the Ir0 layer closest to the interface becoming non-magnetic, while the next layer (Ir1) continues to maintain the AFM structure of the bulk, but with a reduced magnetic moment. The Fermi surface consists of a hole pocket and an electron pocket, located in two different Ir layers (Ir0 and Ir1), with both carriers derived from the [Formula: see text] upper Hubbard band. The presence of both electrons and holes at the [Formula: see text]-doped interface suggests unusual transport properties, leading to possible device applications.
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Affiliation(s)
- Churna Bhandari
- Department of Physics & Astronomy, University of Columbia Missouri, Columbia, MO 65211, United States of America
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15
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Singh G, Jouan A, Herranz G, Scigaj M, Sánchez F, Benfatto L, Caprara S, Grilli M, Saiz G, Couëdo F, Feuillet-Palma C, Lesueur J, Bergeal N. Gap suppression at a Lifshitz transition in a multi-condensate superconductor. NATURE MATERIALS 2019; 18:948-954. [PMID: 31086324 DOI: 10.1038/s41563-019-0354-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2018] [Accepted: 03/21/2019] [Indexed: 06/09/2023]
Abstract
In multi-orbital materials, superconductivity can exhibit several coupled condensates. In this context, quantum confinement in two-dimensional superconducting oxide interfaces offers new degrees of freedom to engineer the band structure and selectively control the occupancy of 3d orbitals by electrostatic doping. Here, we use resonant microwave transport to extract the superfluid stiffness of the (110)-oriented LaAlO3/SrTiO3 interface in the entire phase diagram. We provide evidence of a transition from single-condensate to two-condensate superconductivity driven by continuous and reversible electrostatic doping, which we relate to the Lifshitz transition between 3d bands based on numerical simulations of the quantum well. We find that the superconducting gap is suppressed while the second band is populated, challenging Bardeen-Cooper-Schrieffer theory. We ascribe this behaviour to the existence of superconducting order parameters with opposite signs in the two condensates due to repulsive coupling. Our findings offer an innovative perspective on the possibility to tune and control multiple-orbital physics in superconducting interfaces.
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Affiliation(s)
- G Singh
- Laboratoire de Physique et d'Etude des Matériaux, ESPCI Paris, PSL Research University, CNRS, Paris, France
- Université Pierre and Marie Curie, Sorbonne-Université, Paris, France
| | - A Jouan
- Laboratoire de Physique et d'Etude des Matériaux, ESPCI Paris, PSL Research University, CNRS, Paris, France
- Université Pierre and Marie Curie, Sorbonne-Université, Paris, France
| | - G Herranz
- Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra, Catalonia, Spain
| | - M Scigaj
- Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra, Catalonia, Spain
| | - F Sánchez
- Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra, Catalonia, Spain
| | - L Benfatto
- Institute for Complex Systems (ISC-CNR), UOS Sapienza, Roma, Italy
- Dipartimento di Fisica Università di Roma 'La Sapienza', Roma, Italy
| | - S Caprara
- Institute for Complex Systems (ISC-CNR), UOS Sapienza, Roma, Italy
- Dipartimento di Fisica Università di Roma 'La Sapienza', Roma, Italy
| | - M Grilli
- Institute for Complex Systems (ISC-CNR), UOS Sapienza, Roma, Italy
- Dipartimento di Fisica Università di Roma 'La Sapienza', Roma, Italy
| | - G Saiz
- Laboratoire de Physique et d'Etude des Matériaux, ESPCI Paris, PSL Research University, CNRS, Paris, France
- Université Pierre and Marie Curie, Sorbonne-Université, Paris, France
| | - F Couëdo
- Laboratoire de Physique et d'Etude des Matériaux, ESPCI Paris, PSL Research University, CNRS, Paris, France
- Université Pierre and Marie Curie, Sorbonne-Université, Paris, France
| | - C Feuillet-Palma
- Laboratoire de Physique et d'Etude des Matériaux, ESPCI Paris, PSL Research University, CNRS, Paris, France
- Université Pierre and Marie Curie, Sorbonne-Université, Paris, France
| | - J Lesueur
- Laboratoire de Physique et d'Etude des Matériaux, ESPCI Paris, PSL Research University, CNRS, Paris, France
- Université Pierre and Marie Curie, Sorbonne-Université, Paris, France
| | - N Bergeal
- Laboratoire de Physique et d'Etude des Matériaux, ESPCI Paris, PSL Research University, CNRS, Paris, France.
- Université Pierre and Marie Curie, Sorbonne-Université, Paris, France.
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16
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Khanna U, Rout PK, Mograbi M, Tuvia G, Leermakers I, Zeitler U, Dagan Y, Goldstein M. Symmetry and Correlation Effects on Band Structure Explain the Anomalous Transport Properties of (111) LaAlO_{3}/SrTiO_{3}. PHYSICAL REVIEW LETTERS 2019; 123:036805. [PMID: 31386445 DOI: 10.1103/physrevlett.123.036805] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Indexed: 06/10/2023]
Abstract
The interface between the two insulating oxides SrTiO_{3} and LaAlO_{3} gives rise to a two-dimensional electron system with intriguing transport phenomena, including superconductivity, which are controllable by a gate. Previous measurements on the (001) interface have shown that the superconducting critical temperature, the Hall density, and the frequency of quantum oscillations, vary nonmonotonically and in a correlated fashion with the gate voltage. In this Letter we experimentally demonstrate that the (111) interface features a qualitatively distinct behavior, in which the frequency of Shubnikov-de Haas oscillations changes monotonically, while the variation of other properties is nonmonotonic albeit uncorrelated. We develop a theoretical model, incorporating the different symmetries of these interfaces as well as electronic-correlation-induced band competition. We show that the latter dominates at (001), leading to similar nonmonotonicity in all observables, while the former is more important at (111), giving rise to highly curved Fermi contours, and accounting for all its anomalous transport measurements.
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Affiliation(s)
- Udit Khanna
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, Tel Aviv, 6997801, Israel
| | - P K Rout
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, Tel Aviv, 6997801, Israel
| | - Michael Mograbi
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, Tel Aviv, 6997801, Israel
| | - Gal Tuvia
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, Tel Aviv, 6997801, Israel
| | - Inge Leermakers
- High Field Magnet Laboratory (HFML-EFML), Radboud University, 6525 ED Nijmegen, Netherlands
| | - Uli Zeitler
- High Field Magnet Laboratory (HFML-EFML), Radboud University, 6525 ED Nijmegen, Netherlands
| | - Yoram Dagan
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, Tel Aviv, 6997801, Israel
| | - Moshe Goldstein
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, Tel Aviv, 6997801, Israel
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17
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Wang L, Pan W, Hu WX, Sun DY. Strain-induced indirect-to-direct bandgap transition in an np-type LaAlO 3/SrTiO 3(110) superlattice. Phys Chem Chem Phys 2019; 21:7075-7082. [DOI: 10.1039/c8cp07761d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
By applying uniaxial in-plane strains, an indirect-to-direct bandgap transition occurs in the polar LaAlO3/SrTiO3 (110) superlattices.
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Affiliation(s)
- L. Wang
- Department of Physics
- East China Normal University
- Shanghai 200241
- People's Republic of China
| | - W. Pan
- Department of Physics
- East China Normal University
- Shanghai 200241
- People's Republic of China
| | - W. X. Hu
- The computer Center
- East China Normal University
- Shanghai 200241
- People's Republic of China
| | - D. Y. Sun
- Department of Physics
- East China Normal University
- Shanghai 200241
- People's Republic of China
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18
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Huang Z, Renshaw Wang X, Rusydi A, Chen J, Yang H, Venkatesan T. Interface Engineering and Emergent Phenomena in Oxide Heterostructures. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1802439. [PMID: 30133012 DOI: 10.1002/adma.201802439] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 07/06/2018] [Indexed: 06/08/2023]
Abstract
Complex oxide interfaces have mesmerized the scientific community in the last decade due to the possibility of creating tunable novel multifunctionalities, which are possible owing to the strong interaction among charge, spin, orbital, and structural degrees of freedom. Artificial interfacial modifications, which include defects, formal polarization, structural symmetry breaking, and interlayer interaction, have led to novel properties in various complex oxide heterostructures. These emergent phenomena not only serve as a platform for investigating strong electronic correlations in low-dimensional systems but also provide potentials for exploring next-generation electronic devices with high functionality. Herein, some recently developed strategies in engineering functional oxide interfaces and their emergent properties are reviewed.
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Affiliation(s)
- Zhen Huang
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
| | - Xiao Renshaw Wang
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
| | - Andrivo Rusydi
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
| | - Jingsheng Chen
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
| | - Hyunsoo Yang
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
| | - Thirumalai Venkatesan
- NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117411, Singapore
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19
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Majorana Fermions in One-Dimensional Structures at LaAlO3/SrTiO3 Oxide Interfaces. CONDENSED MATTER 2018. [DOI: 10.3390/condmat3040037] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We study one-dimensional structures that may be formed at the LaAlO 3 /SrTiO 3 oxide interface by suitable top gating. These structures are modeled via a single-band model with Rashba spin-orbit coupling, superconductivity and a magnetic field along the one-dimensional chain. We first discuss the conditions for the occurrence of a topological superconducting phase and the related formation of Majorana fermions at the chain endpoints, highlighting a close similarity between this model and the Kitaev model, which also reflects in a similar condition the formation of a topological phase. Solving the model in real space, we also study the spatial extension of the wave function of the Majorana fermions and how this increases with approaching the limit condition for the topological state. Using a scattering matrix formalism, we investigate the stability of the Majorana fermions in the presence of disorder and discuss the evolution of the topological phase with increasing disorder.
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20
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Li C, Jiang W, Liu M, Hong Y, Xue H, Meng J, Zhang Z, Li Y, Liu K, He L, Dou R, Xiong C, Nie J. Interaction between in-gap states and carriers at the conductive interface between perovskite oxides. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:405002. [PMID: 30152788 DOI: 10.1088/1361-648x/aadd33] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The 2D electron systems of SrTiO3/NdGaO3 (STO/NGO) and amorphous-LaAlO3/SrTiO3/NdGaO3 (a-LAO/STO/NGO) heterojunctions were explored. An obvious interaction between in-gap states (IGSs) and carriers was found. The IGSs can trap a large number of carriers and enhance carrier scattering. As a result of the high density of IGSs in STO, the conductivity of STO/NGO was severely weakened. However, for a-LAO/STO/NGO heterojunctions, the high carrier density can reduce the effect of IGSs through the electrostatic screening effect. The competition between IGSs and the screening effect of carriers results in an insulator-metal transition and a strange temperature dependence of carrier density. We also explored the interaction between IGSs and carriers theoretically. A mathematical description was proposed and the calculated results showed good agreement with experimental findings.
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Affiliation(s)
- Chengjian Li
- Department of Physics, Beijing Normal University, Beijing 100875, People's Republic of China
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21
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Kim T, Kim SI, Joo S, Kim S, Jeon J, Hong J, Doh YJ, Baek SH, Koo HC. A possible superconductor-like state at elevated temperatures near metal electrodes in an LaAlO 3/SrTiO 3 interface. Sci Rep 2018; 8:11558. [PMID: 30069013 PMCID: PMC6070483 DOI: 10.1038/s41598-018-29945-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Accepted: 07/20/2018] [Indexed: 11/09/2022] Open
Abstract
We experimentally investigated the transport properties near metal electrodes installed on a conducting channel in a LaAlO3/SrTiO3 interface. The local region around the Ti and Al electrodes has a higher electrical conductance than that of other regions, where the upper limits of the temperature and magnetic field can be well defined. Beyond these limits, the conductance abruptly decreases, as in the case of a superconductor. The samples with the Ti- or Al-electrode have an upper-limit temperature of approximately 4 K, which is 10 times higher than the conventional superconducting critical temperature of LaAlO3/SrTiO3 interfaces and delta-doped SrTiO3. This phenomenon is explained by the mechanism of electron transfer between the metal electrodes and electronic d-orbitals in the LaAlO3/SrTiO3 interface. The transferred electrons trigger a phase transition to a superconductor-like state. Our results contribute to the deep understanding of the superconductivity in the LaAlO3/SrTiO3 interface and will be helpful for the development of high-temperature interface superconductors.
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Affiliation(s)
- Taeyueb Kim
- Center for Electromagnetic Metrology, Korea Research Institute of Standards and Science, Daejeon, 34113, Korea
| | - Shin-Ik Kim
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 02792, Korea
| | - Sungjung Joo
- Center for Electromagnetic Metrology, Korea Research Institute of Standards and Science, Daejeon, 34113, Korea
| | - Sangsu Kim
- Department of Display and Semiconductor Physics, Korea University, Sejong, 30019, Korea
| | - Jeehoon Jeon
- Department of Display and Semiconductor Physics, Korea University, Sejong, 30019, Korea
- Center of Spintronics, Korea Institute of Science and Technology, Seoul, 02792, Korea
| | - Jinki Hong
- Department of Display and Semiconductor Physics, Korea University, Sejong, 30019, Korea.
| | - Yong-Joo Doh
- Department of Physics and Photon Science, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Korea
| | - Seung-Hyub Baek
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 02792, Korea
- Division of Nano & Information Technology, KIST School, Korea University of Science and Technology, Seoul, 02792, Korea
| | - Hyun Cheol Koo
- Center of Spintronics, Korea Institute of Science and Technology, Seoul, 02792, Korea.
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841, Korea.
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22
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Li D, Lemal S, Gariglio S, Wu Z, Fête A, Boselli M, Ghosez P, Triscone J. Probing Quantum Confinement and Electronic Structure at Polar Oxide Interfaces. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2018; 5:1800242. [PMID: 30128239 PMCID: PMC6097152 DOI: 10.1002/advs.201800242] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Revised: 04/28/2018] [Indexed: 06/08/2023]
Abstract
Polar discontinuities occurring at interfaces between two materials constitute both a challenge and an opportunity in the study and application of a variety of devices. In order to cure the large electric field occurring in such structures, a reconfiguration of the charge landscape sets in at the interface via chemical modifications, adsorbates, or charge transfer. In the latter case, one may expect a local electronic doping of one material: one example is the two-dimensional electron liquid (2DEL) appearing in SrTiO3 once covered by a polar LaAlO3 layer. Here, it is shown that tuning the formal polarization of a (La,Al)1-x (Sr,Ti) x O3 (LASTO:x) overlayer modifies the quantum confinement of the 2DEL in SrTiO3 and its electronic band structure. The analysis of the behavior in magnetic field of superconducting field-effect devices reveals, in agreement with ab initio calculations and self-consistent Poisson-Schrödinger modeling, that quantum confinement and energy splitting between electronic bands of different symmetries strongly depend on the interface total charge densities. These results strongly support the polar discontinuity mechanisms with a full charge transfer to explain the origin of the 2DEL at the celebrated LaAlO3/SrTiO3 interface and demonstrate an effective tool for tailoring the electronic structure at oxide interfaces.
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Affiliation(s)
- Danfeng Li
- Department of Quantum Matter PhysicsUniversity of Geneva24 quai Ernest‐AnsermetCH‐1211Geneva 4Switzerland
| | - Sébastien Lemal
- Theoretical Materials PhysicsQ‐MATCESAMUniversité de LiègeB‐4000LiègeBelgium
| | - Stefano Gariglio
- Department of Quantum Matter PhysicsUniversity of Geneva24 quai Ernest‐AnsermetCH‐1211Geneva 4Switzerland
| | - Zhenping Wu
- Department of Quantum Matter PhysicsUniversity of Geneva24 quai Ernest‐AnsermetCH‐1211Geneva 4Switzerland
- State Key Laboratory of Information Photonics and Optical Communications and School of ScienceBeijing University of Posts and TelecommunicationsBeijing100876China
| | - Alexandre Fête
- Department of Quantum Matter PhysicsUniversity of Geneva24 quai Ernest‐AnsermetCH‐1211Geneva 4Switzerland
| | - Margherita Boselli
- Department of Quantum Matter PhysicsUniversity of Geneva24 quai Ernest‐AnsermetCH‐1211Geneva 4Switzerland
| | - Philippe Ghosez
- Theoretical Materials PhysicsQ‐MATCESAMUniversité de LiègeB‐4000LiègeBelgium
| | - Jean‐Marc Triscone
- Department of Quantum Matter PhysicsUniversity of Geneva24 quai Ernest‐AnsermetCH‐1211Geneva 4Switzerland
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23
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Song K, Ryu S, Lee H, Paudel TR, Koch CT, Park B, Lee JK, Choi SY, Kim YM, Kim JC, Jeong HY, Rzchowski MS, Tsymbal EY, Eom CB, Oh SH. Direct imaging of the electron liquid at oxide interfaces. NATURE NANOTECHNOLOGY 2018; 13:198-203. [PMID: 29402977 DOI: 10.1038/s41565-017-0040-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Accepted: 12/04/2017] [Indexed: 06/07/2023]
Abstract
The breaking of symmetry across an oxide heterostructure causes the electronic orbitals to be reconstructed at the interface into energy states that are different from their bulk counterparts 1 . The detailed nature of the orbital reconstruction critically affects the spatial confinement and the physical properties of the electrons occupying the interfacial orbitals2-4. Using an example of two-dimensional electron liquids forming at LaAlO3/SrTiO3 interfaces5,6 with different crystal symmetry, we show that the selective orbital occupation and spatial quantum confinement of electrons can be resolved with subnanometre resolution using inline electron holography. For the standard (001) interface, the charge density map obtained by inline electron holography shows that the two-dimensional electron liquid is confined to the interface with narrow spatial extension (~1.0 ± 0.3 nm in the half width). On the other hand, the two-dimensional electron liquid formed at the (111) interface shows a much broader spatial extension (~3.3 ± 0.3 nm) with the maximum density located ~2.4 nm away from the interface, in excellent agreement with density functional theory calculations.
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Affiliation(s)
- Kyung Song
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
- Materials Modeling and Characterization Department, Korea Institute of Materials Science (KIMS), Changwon, Republic of Korea
| | - Sangwoo Ryu
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA
| | - Hyungwoo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA
| | - Tula R Paudel
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA
| | - Christoph T Koch
- Department of Physics, Humboldt University of Berlin, Berlin, Germany
| | - Bumsu Park
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
- Department of Energy Science, Sungkyunkwan University (SKKU), Suwon, Republic of Korea
| | - Ja Kyung Lee
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon, Republic of Korea
| | - Si-Young Choi
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
- Materials Modeling and Characterization Department, Korea Institute of Materials Science (KIMS), Changwon, Republic of Korea
| | - Young-Min Kim
- Department of Energy Science, Sungkyunkwan University (SKKU), Suwon, Republic of Korea
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon, Republic of Korea
| | - Jong Chan Kim
- School of Materials Science and Engineering, Ulsan National Institute of Science and Engineering (UNIST), Ulsan, Republic of Korea
| | - Hu Young Jeong
- School of Materials Science and Engineering, Ulsan National Institute of Science and Engineering (UNIST), Ulsan, Republic of Korea
- UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Engineering (UNIST), Ulsan, Republic of Korea
| | - Mark S Rzchowski
- Department of Physics, University of Wisconsin-Madison, Madison, WI, USA
| | - Evgeny Y Tsymbal
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA
| | - Chang-Beom Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA
| | - Sang Ho Oh
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea.
- Department of Energy Science, Sungkyunkwan University (SKKU), Suwon, Republic of Korea.
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24
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Pai YY, Tylan-Tyler A, Irvin P, Levy J. Physics of SrTiO 3-based heterostructures and nanostructures: a review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:036503. [PMID: 29424362 DOI: 10.1088/1361-6633/aa892d] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
This review provides a summary of the rich physics expressed within SrTiO3-based heterostructures and nanostructures. The intended audience is researchers who are working in the field of oxides, but also those with different backgrounds (e.g., semiconductor nanostructures). After reviewing the relevant properties of SrTiO3 itself, we will then discuss the basics of SrTiO3-based heterostructures, how they can be grown, and how devices are typically fabricated. Next, we will cover the physics of these heterostructures, including their phase diagram and coupling between the various degrees of freedom. Finally, we will review the rich landscape of quantum transport phenomena, as well as the devices that elicit them.
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Affiliation(s)
- Yun-Yi Pai
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, United States of America. Pittsburgh Quantum Institute, Pittsburgh, PA 15260, United States of America
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25
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Nanoscale Structural Modulation and Low-temperature Magnetic Response in Mixed-layer Aurivillius-type Oxides. Sci Rep 2018; 8:871. [PMID: 29343705 PMCID: PMC5772624 DOI: 10.1038/s41598-018-19448-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Accepted: 01/02/2018] [Indexed: 12/02/2022] Open
Abstract
Nanoscale structural modulation with different layer numbers in layer-structured complex oxides of the binary Bi4Ti3O12-BiFeO3 system can give rise to intriguing phenomena and extraordinary properties, originating from the correlated interfaces of two different phases with different strain states. In this work, we studied the nanoscale structural modulation induced by Co-substitution in the Aurivillius-type oxide of Bi11Fe3Ti6O33 with a unique and naturally occurred mixed-layer structure. Nanoscale structural evolution via doping occurred from the phase-modulated structure composed of 4- and 5-layer phases to a homogeneous 4-layer structure was clearly observed utilizing x-ray diffraction and electron micro-techniques. Significantly, magnetic response for the samples under various temperatures was recorded and larger magnetic coercive fields (e.g. Hc ∼ 10 kOe at 50 K) were found in the phase-modulated samples. Analyses of the x-ray absorption spectra and magnetic response confirmed that the low-temperature magnetic behaviour should be intrinsic to the phase-modulated structure inside the structural transformation region, mainly arising from structural distortions at the correlated interfaces.
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26
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Wang S, Bai Y, Xie L, Li C, Key JD, Wu D, Wang P, Pan X. Ferroelectric Polarization-Modulated Interfacial Fine Structures Involving Two-Dimensional Electron Gases in Pb(Zr,Ti)O 3/LaAlO 3/SrTiO 3 Heterostructures. ACS APPLIED MATERIALS & INTERFACES 2018; 10:1374-1382. [PMID: 29226675 DOI: 10.1021/acsami.7b14712] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Interfacial fine structures of bare LaAlO3/SrTiO3 (LAO/STO) heterostructures are compared with those of LAO/STO heterostructures capped with upward-polarized Pb(Zr0.1,Ti0.9)O3 (PZTup) or downward-polarized Pb(Zr0.5,Ti0.5)O3 (PZTdown) overlayers by aberration-corrected scanning transmission electron microscopy experiments. By combining the acquired electron energy-loss spectroscopy mapping, we are able to directly observe electron transfer from Ti4+ to Ti3+ and ionic displacements at the interface of bare LAO/STO and PZTdown/LAO/STO heterostructure unit cell by unit cell. No evidence of Ti3+ is observed at the interface of the PZTup/LAO/STO samples. Furthermore, the confinement of the two-dimensional electron gas (2DEG) at the interface is determined by atomic-column spatial resolution. Compared with the bare LAO/STO interface, the 2DEG density at the LAO/STO interface is enhanced or depressed by the PZTdown or PZTup overlayer, respectively. Our microscopy studies shed light on the mechanism of ferroelectric modulation of interfacial transport at polar/nonpolar oxide heterointerfaces, which may facilitate applications of these materials as nonvolatile memory.
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Affiliation(s)
- Shuangbao Wang
- National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, China
- Collaborative Innovation Center of Sustainable Energy Materials, Guangxi University , Nanning 530004, China
| | - Yuhang Bai
- National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, China
| | - Lin Xie
- National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, China
| | - Chen Li
- National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, China
| | - Julian D Key
- Collaborative Innovation Center of Sustainable Energy Materials, Guangxi University , Nanning 530004, China
| | - Di Wu
- National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, China
| | - Peng Wang
- National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, China
| | - Xiaoqing Pan
- Department of Physics and Astronomy and Department of Chemical Engineering and Materials Science, University of California , Irvine, California 92697, United States
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27
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Li CJ, Xue HX, Qu GL, Shen SC, Hong YP, Wang XX, Liu MR, Jiang WM, Badica P, He L, Dou RF, Xiong CM, Lü WM, Nie JC. Influence of In-Gap States on the Formation of Two-Dimensional Election Gas at ABO 3/SrTiO 3 Interfaces. Sci Rep 2018; 8:195. [PMID: 29317754 PMCID: PMC5760580 DOI: 10.1038/s41598-017-18583-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Accepted: 12/13/2017] [Indexed: 12/01/2022] Open
Abstract
We explored in-gap states (IGSs) in perovskite oxide heterojunction films. We report that IGSs in these films play a crucial role in determining the formation and properties of interfacial two-dimensional electron gas (2DEG). We report that electron trapping by IGSs opposes charge transfer from the film to the interface. The IGS in films yielded insulating interfaces with polar discontinuity and explained low interface carrier density of conducting interfaces. An ion trapping model was proposed to explain the physics of the IGSs and some experimental findings, such as the unexpected formation of 2DEG at the initially insulating LaCrO3/SrTiO3 interface and the influence of substitution layers on 2DEG.
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Affiliation(s)
- Cheng-Jian Li
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Hong-Xia Xue
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Guo-Liang Qu
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Sheng-Chun Shen
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Yan-Peng Hong
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Xin-Xin Wang
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Ming-Rui Liu
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Wei-Min Jiang
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Petre Badica
- National Institute of Materials Physics, Atomistilor 405A, Magurele, Ilfov, 077125, Romania
| | - Lin He
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Rui-Fen Dou
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Chang-Min Xiong
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Wei-Ming Lü
- Condensed Matter Science and Technology Institute, Harbin Institute of Technology, Harbin, 150001, China
| | - Jia-Cai Nie
- Department of Physics, Beijing Normal University, Beijing, 100875, China.
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28
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Zhou F, Liu Y, Lai Z, Liao M, Zhou Y, Huang Y, Zhu J. Quantum confined two-dimensional electron/hole gas switching by facet orientation of perovskite oxides. RSC Adv 2018; 8:20477-20482. [PMID: 35542364 PMCID: PMC9080832 DOI: 10.1039/c8ra03928c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Accepted: 05/29/2018] [Indexed: 11/21/2022] Open
Abstract
The Polar discontinuity at heterointerface and the bare surface reconstructs the electronic phase of perovskite oxides.
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Affiliation(s)
- Fei Zhou
- School of Materials Science and Engineering
- Harbin Institute of Technology
- Harbin
- China
- MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage
| | - Yong Liu
- School of Materials Science and Engineering
- Harbin Institute of Technology
- Harbin
- China
- National Key Laboratory for Precision Hot Processing of Metals
| | - Zhonghong Lai
- Analysis and Testing Center
- Harbin Institute of Technology
- Harbin
- China
| | - Mingqing Liao
- School of Materials Science and Engineering
- Harbin Institute of Technology
- Harbin
- China
| | - Yi Zhou
- School of Materials Science and Engineering
- Harbin Institute of Technology
- Harbin
- China
| | - Yudong Huang
- MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage
- School of Chemistry and Chemical Engineering, Harbin Institute of Technology
- Harbin
- China
| | - Jingchuan Zhu
- School of Materials Science and Engineering
- Harbin Institute of Technology
- Harbin
- China
- National Key Laboratory of Science and Technology on Advanced Composites in Special Environments
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29
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Mawrie A, Verma S, Ghosh TK. Electrical and thermoelectric transport properties of two-dimensional fermionic systems with k-cubic spin-orbit coupling. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:465303. [PMID: 29067916 DOI: 10.1088/1361-648x/aa89b9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We investigate the effect of k-cubic spin-orbit interaction on the electrical and thermoelectric transport properties of two-dimensional fermionic systems. We obtain exact analytical expressions of the inverse relaxation time (IRT) and the Drude conductivity for long-range Coulomb and short-range delta scattering potentials. The IRT reveals that the scattering is completely suppressed along the three directions [Formula: see text] with [Formula: see text]. We also obtain analytical results of the thermopower and thermal conductivity at low temperature. The thermoelectric transport coefficients obey the Wiedemann-Franz law, even in the presence of k-cubic Rashba spin-orbit interaction (RSOI) at low temperature. In the presence of a quantizing magnetic field, the signature of the RSOI is revealed through the appearance of the beating pattern in the Shubnikov-de Haas (SdH) oscillations of thermopower and thermal conductivity in the low magnetic field regime. The empirical formulae for the SdH oscillation frequencies accurately describe the locations of the beating nodes. The beating pattern in magnetothermoelectric measurement can be used to extract the spin-orbit coupling constant.
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Affiliation(s)
- Alestin Mawrie
- Department of Physics, Indian Institute of Technology-Kanpur, Kanpur-208 016, India
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30
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Plumb NC, Radović M. Angle-resolved photoemission spectroscopy studies of metallic surface and interface states of oxide insulators. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:433005. [PMID: 28961143 DOI: 10.1088/1361-648x/aa833f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Over the last decade, conducting states embedded in insulating transition metal oxides (TMOs) have served as gateways to discovering and probing surprising phenomena that can emerge in complex oxides, while also opening opportunities for engineering advanced devices. These states are commonly realized at thin film interfaces, such as the well-known case of LaAlO3 (LAO) grown on SrTiO3 (STO). In recent years, the use of angle-resolved photoemission spectroscopy (ARPES) to investigate the k-space electronic structure of such materials led to the discovery that metallic states can also be formed on the bare surfaces of certain TMOs. In this topical review, we report on recent studies of low-dimensional metallic states confined at insulating oxide surfaces and interfaces as seen from the perspective of ARPES, which provides a direct view of the occupied band structure. While offering a fairly broad survey of progress in the field, we draw particular attention to STO, whose surface is so far the best-studied, and whose electronic structure is probably of the most immediate interest, given the ubiquitous use of STO substrates as the basis for conducting oxide interfaces. The ARPES studies provide crucial insights into the electronic band structure, orbital character, dimensionality/confinement, spin structure, and collective excitations in STO surfaces and related oxide surface/interface systems. The obtained knowledge increases our understanding of these complex materials and gives new perspectives on how to manipulate their properties.
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Affiliation(s)
- Nicholas C Plumb
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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31
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Wang L, Kim R, Kim Y, Kim CH, Hwang S, Cho MR, Shin YJ, Das S, Kim JR, Kalinin SV, Kim M, Yang SM, Noh TW. Electronic-Reconstruction-Enhanced Tunneling Conductance at Terrace Edges of Ultrathin Oxide Films. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2017; 29:1702001. [PMID: 29024168 DOI: 10.1002/adma.201702001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Revised: 09/06/2017] [Indexed: 06/07/2023]
Abstract
Quantum mechanical tunneling of electrons across ultrathin insulating oxide barriers has been studied extensively for decades due to its great potential in electronic-device applications. In the few-nanometers-thick epitaxial oxide films, atomic-scale structural imperfections, such as the ubiquitously existed one-unit-cell-high terrace edges, can dramatically affect the tunneling probability and device performance. However, the underlying physics has not been investigated adequately. Here, taking ultrathin BaTiO3 films as a model system, an intrinsic tunneling-conductance enhancement is reported near the terrace edges. Scanning-probe-microscopy results demonstrate the existence of highly conductive regions (tens of nanometers wide) near the terrace edges. First-principles calculations suggest that the terrace-edge geometry can trigger an electronic reconstruction, which reduces the effective tunneling barrier width locally. Furthermore, such tunneling-conductance enhancement can be discovered in other transition metal oxides and controlled by surface-termination engineering. The controllable electronic reconstruction can facilitate the implementation of oxide electronic devices and discovery of exotic low-dimensional quantum phases.
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Affiliation(s)
- Lingfei Wang
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Republic of Korea
| | - Rokyeon Kim
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Republic of Korea
| | - Yoonkoo Kim
- Department of Materials Science and Engineering and Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Choong H Kim
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Republic of Korea
| | - Sangwoon Hwang
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Republic of Korea
| | - Myung Rae Cho
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Republic of Korea
| | - Yeong Jae Shin
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Republic of Korea
| | - Saikat Das
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Republic of Korea
| | - Jeong Rae Kim
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Republic of Korea
| | - Sergei V Kalinin
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Miyoung Kim
- Department of Materials Science and Engineering and Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Sang Mo Yang
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
- Department of Physics, Sookmyung Women's University, Seoul, 04310, Republic of Korea
| | - Tae Won Noh
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Republic of Korea
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32
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Smink AEM, de Boer JC, Stehno MP, Brinkman A, van der Wiel WG, Hilgenkamp H. Gate-Tunable Band Structure of the LaAlO_{3}-SrTiO_{3} Interface. PHYSICAL REVIEW LETTERS 2017; 118:106401. [PMID: 28339281 DOI: 10.1103/physrevlett.118.106401] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Indexed: 06/06/2023]
Abstract
The two-dimensional electron system at the interface between LaAlO_{3} and SrTiO_{3} has several unique properties that can be tuned by an externally applied gate voltage. In this work, we show that this gate tunability extends to the effective band structure of the system. We combine a magnetotransport study on top-gated Hall bars with self-consistent Schrödinger-Poisson calculations and observe a Lifshitz transition at a density of 2.9×10^{13}cm^{-2}. Above the transition, the carrier density of one of the conducting bands decreases with increasing gate voltage. This surprising decrease is accurately reproduced in the calculations if electronic correlations are included. These results provide a clear, intuitive picture of the physics governing the electronic structure at complex-oxide interfaces.
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Affiliation(s)
- A E M Smink
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - J C de Boer
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - M P Stehno
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - A Brinkman
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - W G van der Wiel
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - H Hilgenkamp
- MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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33
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Maniv E, Dagan Y, Goldstein M. Correlation-Induced Band Competition in SrTiO3/LaAlO3. ACTA ACUST UNITED AC 2017. [DOI: 10.1557/adv.2017.92] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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34
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Mawrie A, Kanti Ghosh T. Optical conductivity of a 2DEG with anisotropic Rashba interaction at the interface of LaAlO3/SrTiO3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:425302. [PMID: 27554399 DOI: 10.1088/0953-8984/28/42/425302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We study optical conductivity of a two-dimensional electron gas with anisotropic k-cubic Rashba spin-orbit interaction formed at the LaAlO3/SrTiO3 interface. The anisotropic spin splitting energy gives rise to different features of the optical conductivity in comparison to the isotropic k-cubic Rashba spin-orbit interaction. For large carrier density and strong spin-orbit couplings, the density dependence of Drude weight deviates from the linear behavior. The charge and optical conductivities remain isotropic despite anisotropic nature of the Fermi contours. An infinitesimally small photon energy would suffice to initiate inter-band optical transitions due to degeneracy along certain directions in momentum space. The optical conductivity shows a single peak at a given photon energy depending on the system parameters and then falls off to zero at higher photon energy. These features are lacking for systems with isotropic k-cubic Rashba spin-orbit coupling. These striking features can be used to extract the information about nature of the spin-orbit interaction experimentally and illuminate some light on the orbital origin of the two-dimensional electron gas.
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Affiliation(s)
- Alestin Mawrie
- Department of Physics, Indian Institute of Technology-Kanpur, Kanpur-208 016, India
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35
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Guo H, Saidi WA, Zhao J. Tunability of the two-dimensional electron gas at the LaAlO 3/SrTiO 3 interface by strain-induced ferroelectricity. Phys Chem Chem Phys 2016; 18:28474-28484. [PMID: 27711681 DOI: 10.1039/c6cp04769f] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The two-dimensional electron gas (2DEG) formed at the interface between two insulating materials LaAlO3 (LAO) and SrTiO3 (STO) has recently generated a lot of interest. Here, based on first-principles density functional theory calculations, we investigate the existence and stability of the 2DEG under the application of a biaxial strain on the LAO/STO(001) heterostructure. The compressive strain induces ferroelectric (FE) polarization in STO, which allows for the tunability of the 2DEG by reversing the STO polarization orientation. We show that the formation of the 2DEG is unstable when LAO and STO have the same polarization direction. On the other hand, the 2DEG will always form if the two polarizations are in the opposite directions regardless of the LAO thickness, which is in contrast to the unstrained interface that has a critical thickness for stabilizing the 2DEG. We show that the underpinnings of this behavior are due to charge passivation and band gap alignment.
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Affiliation(s)
- Hongli Guo
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China. and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Wissam A Saidi
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
| | - Jin Zhao
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China. and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Department of Physics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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36
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Han K, Palina N, Zeng SW, Huang Z, Li CJ, Zhou WX, Wan DY, Zhang LC, Chi X, Guo R, Chen JS, Venkatesan T, Rusydi A, Ariando A. Controlling Kondo-like Scattering at the SrTiO3-based Interfaces. Sci Rep 2016; 6:25455. [PMID: 27147407 PMCID: PMC4857089 DOI: 10.1038/srep25455] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 04/13/2016] [Indexed: 11/08/2022] Open
Abstract
The observation of magnetic interaction at the interface between nonmagnetic oxides has attracted much attention in recent years. In this report, we show that the Kondo-like scattering at the SrTiO3-based conducting interface is enhanced by increasing the lattice mismatch and growth oxygen pressure PO2. For the 26-unit-cell LaAlO3/SrTiO3 (LAO/STO) interface with lattice mismatch being 3.0%, the Kondo-like scattering is observed when PO2 is beyond 1 mTorr. By contrast, when the lattice mismatch is reduced to 1.0% at the (La0.3Sr0.7)(Al0.65Ta0.35)O3/SrTiO3 (LSAT/STO) interface, the metallic state is always preserved up to PO2 of 100 mTorr. The data from Hall measurement and X-ray absorption near edge structure (XANES) spectroscopy reveal that the larger amount of localized Ti(3+) ions are formed at the LAO/STO interface compared to LSAT/STO. Those localized Ti(3+) ions with unpaired electrons can be spin-polarized to scatter mobile electrons, responsible for the Kondo-like scattering observed at the LAO/STO interface.
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Affiliation(s)
- K. Han
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - N. Palina
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore
| | - S. W. Zeng
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - Z. Huang
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
| | - C. J. Li
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
| | - W. X. Zhou
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - D.-Y. Wan
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - L. C. Zhang
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
| | - X. Chi
- Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore
| | - R. Guo
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
- Department of Material Science & Engineering, National University of Singapore, Singapore 117575, Singapore
| | - J. S. Chen
- Department of Material Science & Engineering, National University of Singapore, Singapore 117575, Singapore
| | - T. Venkatesan
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
- Department of Material Science & Engineering, National University of Singapore, Singapore 117575, Singapore
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Singapore
- National University of Singapore Graduate School for Integrative Sciences and Engineering (NGS), 28 Medical Drive, Singapore 117456, Singapore
| | - A. Rusydi
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
- Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore
| | - A Ariando
- NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore
- Department of Physics, National University of Singapore, Singapore 117542, Singapore
- National University of Singapore Graduate School for Integrative Sciences and Engineering (NGS), 28 Medical Drive, Singapore 117456, Singapore
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37
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Chung SB, Chan C, Yao H. Dislocation Majorana zero modes in perovskite oxide 2DEG. Sci Rep 2016; 6:25184. [PMID: 27139319 PMCID: PMC4853714 DOI: 10.1038/srep25184] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Accepted: 04/12/2016] [Indexed: 11/28/2022] Open
Abstract
Much of the current experimental efforts for detecting Majorana zero modes have been centered on probing the boundary of quantum wires with strong spin-orbit coupling. The same type of Majorana zero mode can also be realized at crystalline dislocations in 2D superconductors with the nontrivial weak topological indices. Unlike at an Abrikosov vortex, at such a dislocation, there is no other low-lying midgap state than the Majorana zero mode so that it avoids usual complications encountered in experimental detections such as scanning tunneling microscope (STM) measurements. We will show that, using the anisotropic dispersion of the t2g orbitals of Ti or Ta atoms, such a weak topological superconductivity can be realized when the surface two-dimensional electronic gas (2DEG) of SrTiO3 or KTaO3 becomes superconducting, which can occur through either intrinsic pairing or proximity to existing s-wave superconductors.
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Affiliation(s)
- Suk Bum Chung
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 151-742, Republic of Korea.,Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
| | - Cheung Chan
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
| | - Hong Yao
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
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38
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Dai W, Adhikari S, Garcia-Castro AC, Romero AH, Lee H, Lee JW, Ryu S, Eom CB, Cen C. Tailoring LaAlO3/SrTiO3 Interface Metallicity by Oxygen Surface Adsorbates. NANO LETTERS 2016; 16:2739-2743. [PMID: 26928809 DOI: 10.1021/acs.nanolett.6b00421] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report an oxygen surface adsorbates induced metal-insulator transition at the LaAlO3/SrTiO3 interfaces. The observed effects were attributed to the terminations of surface Al sites and the resultant electron-accepting surface states. By controlling the local oxygen adsorptions, we successfully demonstrated the nondestructive patterning of the interface two-dimensional electron gas (2DEG). The obtained 2DEG structures are stable in air and also robust against general solvent treatments. This study provides new insights into the metal-insulator transition mechanism at the complex oxide interfaces and also a highly efficient technique for tailoring the interface properties.
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Affiliation(s)
- Weitao Dai
- Department of Physics and Astronomy, West Virginia University , Morgantown, West Virginia 26506, United States
| | - Sanjay Adhikari
- Department of Physics and Astronomy, West Virginia University , Morgantown, West Virginia 26506, United States
| | - Andrés Camilo Garcia-Castro
- Physique Théorique des Matériaux, Université de Liège , B-4000 Sart-Tilman, Belgium
- Centro de Investigación y Estudios Avanzados del IPN , MX-76230 Querétaro, México
| | - Aldo H Romero
- Department of Physics and Astronomy, West Virginia University , Morgantown, West Virginia 26506, United States
| | - Hyungwoo Lee
- Department of Material Science and Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States
| | - Jung-Woo Lee
- Department of Material Science and Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States
| | - Sangwoo Ryu
- Department of Material Science and Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States
| | - Chang-Beom Eom
- Department of Material Science and Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States
| | - Cheng Cen
- Department of Physics and Astronomy, West Virginia University , Morgantown, West Virginia 26506, United States
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39
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Moon SY, Moon CW, Chang HJ, Kim T, Kang CY, Choi HJ, Kim JS, Baek SH, Jang HW. Thermal stability of 2DEG at amorphous LaAlO 3/crystalline SrTiO 3 heterointerfaces. NANO CONVERGENCE 2016; 3:7. [PMID: 28191417 PMCID: PMC5271142 DOI: 10.1186/s40580-016-0067-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 02/10/2016] [Indexed: 06/06/2023]
Abstract
At present, the generation of heterostructures with two dimensional electron gas (2DEG) in amorphous LaAlO3 (a-LAO)/SrTiO3 (STO) has been achieved. Herein, we analysed thermal stability of 2DEG at a-LAO/STO interfaces in comparison with 2DEG at crystalline LaAlO3 (c-LAO)/STO interfaces. To create 2DEG at LAO/STO interface, regardless of growing temperature from 25 to 700 °C, we found that environment with oxygen deficient during the deposition of LAO overlayer is essentially required. That indicates that the oxygen-poor condition in the system is more essential than the crystalline nature of LAO layer. 2DEG at a-LAO/STO interface is depleted upon ex situ annealing at 300 °C under 300 Torr of oxygen pressure, while that in c-LAO/STO interface is still maintained. Our result suggests that the LAO overlayer crystallinity critically affects the thermal-annealing-induced depletion of 2DEG at a-LAO/STO interface rather than the generation of 2DEG. We clearly provide that amorphous TiOx can efficiently prevent the thermal degradation of 2DEG at the a-LAO/STO interface, which gives a cornerstone for achieving thermal-stable 2DEG at a-LAO/STO interface.
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Affiliation(s)
- Seon Young Moon
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 136-791 Republic of Korea
- Department of Materials Science and Engineering, Yonsei University, Seoul, 120-749 Republic of Korea
| | - Cheon Woo Moon
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 151-744 Republic of Korea
| | - Hye Jung Chang
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 136-791 Republic of Korea
- Department of Nanomaterials Science and Technology, Korea University of Science and Technology, Daejeon, 305-350 Republic of Korea
| | - Taemin Kim
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 151-744 Republic of Korea
| | - Chong-Yun Kang
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 136-791 Republic of Korea
- Department of Nanomaterials Science and Technology, Korea University of Science and Technology, Daejeon, 305-350 Republic of Korea
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 136-701 Republic of Korea
| | - Heon-Jin Choi
- Department of Materials Science and Engineering, Yonsei University, Seoul, 120-749 Republic of Korea
| | - Jin-Sang Kim
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 136-791 Republic of Korea
| | - Seung-Hyub Baek
- Center for Electronic Materials, Korea Institute of Science and Technology, Seoul, 136-791 Republic of Korea
- Department of Nanomaterials Science and Technology, Korea University of Science and Technology, Daejeon, 305-350 Republic of Korea
| | - Ho Won Jang
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 151-744 Republic of Korea
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40
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Guo H, Saidi WA, Yang J, Zhao J. Nano-scale polar-nonpolar oxide heterostructures for photocatalysis. NANOSCALE 2016; 8:6057-6063. [PMID: 26932200 DOI: 10.1039/c5nr08689b] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We proposed based on first principles density functional theory calculations that a nano-scale thin film based on a polar-nonpolar transition-metal oxide heterostructure can be used as a highly-efficient photocatalyst. This is demonstrated using a SrTiO3/LaAlO3/SrTiO3 sandwich-like heterostructure with photocatalytic activity in the near-infrared region. The effect of the polar nature of LaAlO3 is two-fold. First, the induced electrostatic field accelerates the photo-generated electrons and holes into opposite directions and minimizes their recombination rates. Hence, the reduction and oxidation reactions can be instigated at the SrTiO3 surfaces located on the opposite sides of the heterostructure. Second, the electric field reduces the band gap of the system making it photoactive in the infrared region. We also show that charge separation can be enhanced by using compressive strain engineering that creates ferroelectric instability in STO. The proposed setup is ideal for tandem oxide photocatalysts especially when combined with photoactive polar materials.
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Affiliation(s)
- Hongli Guo
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Wissam A Saidi
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
| | - Jinlong Yang
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jin Zhao
- ICQD/Hefei National Laboratory for Physical Sciences at Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China and Department of Physics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
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41
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Behtash M, Nazir S, Wang Y, Yang K. Polarization effects on the interfacial conductivity in LaAlO3/SrTiO3heterostructures: a first-principles study. Phys Chem Chem Phys 2016; 18:6831-8. [DOI: 10.1039/c5cp07581e] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
First-principles calculations predict the normalized electron carrier density (μ/μ0), the mobility (m*/m0), and the conductivity (σ/σ0) in LaAlO3/SrTiO3as a function of uniaxial strain.
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Affiliation(s)
- Maziar Behtash
- Department of NanoEngineering
- University of California
- La Jolla
- USA
| | - Safdar Nazir
- Department of NanoEngineering
- University of California
- La Jolla
- USA
| | - Yaqin Wang
- Department of NanoEngineering
- University of California
- La Jolla
- USA
| | - Kesong Yang
- Department of NanoEngineering
- University of California
- La Jolla
- USA
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42
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Abstract
The thermoelectric properties of the (001) n-type 6.5STO/1.5LAO interface were investigated by means of the all-electron full-potential method based on the semi-classical Boltzmann theory.
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Affiliation(s)
- A. H. Reshak
- New Technologies – Research Centre
- University of West Bohemia
- 306 14 Pilsen
- Czech Republic
- School of Material Engineering
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43
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Electronic Structure of Oxide Interfaces: A Comparative Analysis of GdTiO3/SrTiO3 and LaAlO3/SrTiO3 Interfaces. Sci Rep 2015; 5:18647. [PMID: 26689360 PMCID: PMC4686895 DOI: 10.1038/srep18647] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2015] [Accepted: 11/17/2015] [Indexed: 11/20/2022] Open
Abstract
Emergent phases in the two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides have attracted great attention in the past decade. We present ab-initio electronic structure calculations for the interface between a Mott insulator GdTiO3 (GTO) and a band insulator SrTiO3 (STO) and compare our results with those for the widely studied LaAlO3/SrTiO3 (LAO/STO) interface between two band insulators. Our GTO/STO results are in excellent agreement with experiments, but qualitatively different from LAO/STO. We find an interface carrier density of 0.5 e−/Ti, independent of GTO thickness in both superlattice and thin film geometries, in contrast to LAO/STO. The superlattice geometry in LAO/STO offers qualitatively the same result as in GTO/STO. On the other hand, for a thin film geometry, the interface carrier density builds up only beyond a threshold thickness of LAO. The positive charge at the vacuum surface that compensates the 2DEG at the interface also exhibits distinct behaviors in the two systems. The compensating positive charge at the exposed surface of GTO charge disproportionates due to correlation effect making the surface insulating as opposed to that in LAO which remains metallic within band theory and presumably becomes insulating due to surface disorder or surface reconstruction.
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44
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Renshaw Wang X, Sun L, Huang Z, Lü WM, Motapothula M, Annadi A, Liu ZQ, Zeng SW, Venkatesan T, Ariando. Parallel charge sheets of electron liquid and gas in La0.5Sr0.5TiO3/SrTiO3 heterostructures. Sci Rep 2015; 5:18282. [PMID: 26669575 PMCID: PMC4680910 DOI: 10.1038/srep18282] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Accepted: 09/14/2015] [Indexed: 12/05/2022] Open
Abstract
We show here a new phenomenon in La0.5Sr0.5TiO3/SrTiO3 (LSTO/STO) heterostructures; that is a coexistence of three-dimensional electron liquid (3DEL) and 2D electron gas (2DEG), separated by an intervening insulating LSTO layer. The two types of carriers were revealed through multi-channel analysis of the evolution of nonlinear Hall effect as a function of film thickness, temperature and back gate voltage. We demonstrate that the 3D electron originates from La doping in LSTO film and the 2D electron at the surface of STO is due to the polar field in the intervening insulating layer. As the film thickness is reduced below a critical thickness of 6 unit cells (uc), an abrupt metal-to-insulator transition (MIT) occurs without an intermediate semiconducting state. The properties of the LSTO layer grown on different substrates suggest that the insulating phase of the intervening layer is a result of interface strain induced by the lattice mismatch between the film and substrate. Further, by fitting the magnetoresistance (MR) curves, the 6 unit cell thick LSTO is shown to exhibit spin-orbital coupling. These observations point to new functionalities, in addition to magnetism and superconductivity in STO-based systems, which could be exploited in a multifunctional context.
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Affiliation(s)
- X Renshaw Wang
- NUSNNI-Nanocore, National University of Singapore, 117411 Singapore.,Department of Physics, National University of Singapore, 117542 Singapore.,Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, P.O. BOX 217, 7500 AE Enschede, The Netherlands
| | - L Sun
- NUSNNI-Nanocore, National University of Singapore, 117411 Singapore
| | - Z Huang
- NUSNNI-Nanocore, National University of Singapore, 117411 Singapore.,Department of Physics, National University of Singapore, 117542 Singapore
| | - W M Lü
- NUSNNI-Nanocore, National University of Singapore, 117411 Singapore.,Department of Physics, National University of Singapore, 117542 Singapore
| | - M Motapothula
- NUSNNI-Nanocore, National University of Singapore, 117411 Singapore.,Department of Physics, National University of Singapore, 117542 Singapore
| | - A Annadi
- NUSNNI-Nanocore, National University of Singapore, 117411 Singapore.,Department of Physics, National University of Singapore, 117542 Singapore
| | - Z Q Liu
- NUSNNI-Nanocore, National University of Singapore, 117411 Singapore.,Department of Physics, National University of Singapore, 117542 Singapore
| | - S W Zeng
- NUSNNI-Nanocore, National University of Singapore, 117411 Singapore.,Department of Physics, National University of Singapore, 117542 Singapore
| | - T Venkatesan
- NUSNNI-Nanocore, National University of Singapore, 117411 Singapore.,Department of Physics, National University of Singapore, 117542 Singapore.,Department of Electrical and Computer Engineering, National University of Singapore, 117576 Singapore.,National University of Singapore Graduate School for Integrative Sciences and Engineering (NGS), 28 Medical Drive, Singapore 117456, Singapore
| | - Ariando
- NUSNNI-Nanocore, National University of Singapore, 117411 Singapore.,Department of Physics, National University of Singapore, 117542 Singapore.,National University of Singapore Graduate School for Integrative Sciences and Engineering (NGS), 28 Medical Drive, Singapore 117456, Singapore
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45
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Salvinelli G, Drera G, Giampietri A, Sangaletti L. Layer-Resolved Cation Diffusion and Stoichiometry at the LaAlO3/SrTiO3 Heterointerface Probed by X-ray Photoemission Experiments and Site Occupancy Modeling. ACS APPLIED MATERIALS & INTERFACES 2015; 7:25648-25657. [PMID: 26559612 DOI: 10.1021/acsami.5b06094] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The layer-resolved cation occupancy for different conducting and insulating interfaces of LaAlO3 (LAO) thin films on SrTiO3 (STO) has been determined by angle-resoled X-ray photoelectron spectroscopy (AR-XPS). Three STO interfaces with LAO have been considered, namely, a conducting interface with a 5 unit cell (u.c.) LAO layer, an insulating interface with a 5 u.c. LAO layer, and an insulating interface with a 3 u.c. LAO layer. Considering inelastic and elastic scattering processes in the transport approximation, the core-level signal attenuation has been modeled on the basis of Monte Carlo calculations of the electron trajectories across the heterostructures. Different effects involving cation stoichiometry and diffusion through the interface have been considered to interpret data. Beyond a mere abrupt interface modeling, the LaAlO3/SrTiO3 heterojunction is shown to host cation diffusion processes within 3-4 unit cells in the bulk layer, along with a clear Sr substoichiometry, an issue so far virtually neglected in the analysis of these systems. The present results show the capability of the AR-XPS modeling to explore element-sensitive properties at the oxide interfaces, matching and completing the information that can be provided by probes based on electron microscopy or X-ray scattering.
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Affiliation(s)
- Gabriele Salvinelli
- Interdisciplinary Laboratories for Advanced Materials Physics (I-LAMP) and Dipartimento di Matematica e Fisica, Università Cattolica del Sacro Cuore , via dei Musei 41, 25121 Brescia, Italy
| | - Giovanni Drera
- Interdisciplinary Laboratories for Advanced Materials Physics (I-LAMP) and Dipartimento di Matematica e Fisica, Università Cattolica del Sacro Cuore , via dei Musei 41, 25121 Brescia, Italy
| | - Alessio Giampietri
- Interdisciplinary Laboratories for Advanced Materials Physics (I-LAMP) and Dipartimento di Matematica e Fisica, Università Cattolica del Sacro Cuore , via dei Musei 41, 25121 Brescia, Italy
| | - Luigi Sangaletti
- Interdisciplinary Laboratories for Advanced Materials Physics (I-LAMP) and Dipartimento di Matematica e Fisica, Università Cattolica del Sacro Cuore , via dei Musei 41, 25121 Brescia, Italy
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46
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Labram JG, Lin YH, Anthopoulos TD. Exploring Two-Dimensional Transport Phenomena in Metal Oxide Heterointerfaces for Next-Generation, High-Performance, Thin-Film Transistor Technologies. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2015; 11:5472-5482. [PMID: 26349850 DOI: 10.1002/smll.201501350] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Revised: 06/16/2015] [Indexed: 06/05/2023]
Abstract
In the last decade, metal oxides have emerged as a fascinating class of electronic material, exhibiting a wide range of unique and technologically relevant characteristics. For example, thin-film transistors formed from amorphous or polycrystalline metal oxide semiconductors offer the promise of low-cost, large-area, and flexible electronics, exhibiting performances comparable to or in excess of incumbent silicon-based technologies. Atomically flat interfaces between otherwise insulating or semiconducting complex oxides, are also found to be highly conducting, displaying 2-dimensional (2D) charge transport properties, strong correlations, and even superconductivity. Field-effect devices employing such carefully engineered interfaces are hoped to one day compete with traditional group IV or III-V semiconductors for use in the next-generation of high-performance electronics. In this Concept article we provide an overview of the different metal oxide transistor technologies and potential future research directions. In particular, we look at the recent reports of multilayer oxide thin-film transistors and the possibility of 2D electron transport in these disordered/polycrystalline systems and discuss the potential of the technology for applications in large-area electronics.
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Affiliation(s)
- John G Labram
- Department of Physics and Centre for Plastic Electronics, Blackett Laboratory, Imperial College London, London, SW7 2BW, UK
| | - Yen-Hung Lin
- Department of Physics and Centre for Plastic Electronics, Blackett Laboratory, Imperial College London, London, SW7 2BW, UK
| | - Thomas D Anthopoulos
- Department of Physics and Centre for Plastic Electronics, Blackett Laboratory, Imperial College London, London, SW7 2BW, UK
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47
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Universal electronic structure of polar oxide hetero-interfaces. Sci Rep 2015; 5:14506. [PMID: 26411304 PMCID: PMC4585978 DOI: 10.1038/srep14506] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Accepted: 08/26/2015] [Indexed: 11/09/2022] Open
Abstract
The electronic properties of NdGaO3/SrTiO3, LaGaO3/SrTiO3, and LaAlO3/SrTiO3 interfaces, all showing an insulator-to-metal transition as a function of the overlayer-thickness, are addressed in a comparative study based on x-ray absorption, x-ray photoemission and resonant photoemission spectroscopy. The nature of the charge carriers, their concentration and spatial distribution as well as the interface band alignments and the overall interface band diagrams are studied and quantitatively evaluated. The behavior of the three analyzed heterostructures is found to be remarkably similar. The valence band edge of all the three overlayers aligns to that of bulk SrTiO3. The near-interface SrTiO3 layer is affected, at increasing overlayer thickness, by the building-up of a confining potential. This potential bends both the valence and the conduction band downwards. The latter one crossing the Fermi energy in the proximity of the interface and determines the formation of an interfacial band offset growing as a function of thickness. Quite remarkably, but in agreement with previous reports for LaAlO3/SrTiO3, no electric field is detected inside any of the polar overlayers. The essential phenomenology emerging from our findings is discussed on the base of different alternative scenarios regarding the origin of interface carriers and their interaction with an intense photon beam.
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48
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Kamerbeek AM, Högl P, Fabian J, Banerjee T. Electric Field Control of Spin Lifetimes in Nb-SrTiO_{3} by Spin-Orbit Fields. PHYSICAL REVIEW LETTERS 2015; 115:136601. [PMID: 26451572 DOI: 10.1103/physrevlett.115.136601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Indexed: 06/05/2023]
Abstract
We show electric field control of the spin accumulation at the interface of the oxide semiconductor Nb-SrTiO_{3} with Co/AlO_{x} spin injection contacts at room temperature. The in-plane spin lifetime τ_{∥}, as well as the ratio of the out-of-plane to in-plane spin lifetime τ_{⊥}/τ_{∥}, is manipulated by the built-in electric field at the semiconductor surface, without any additional gate contact. The origin of this manipulation is attributed to Rashba spin orbit fields (SOFs) at the Nb-SrTiO_{3} surface and shown to be consistent with theoretical model calculations based on SOF spin flip scattering. Additionally, the junction can be set in a high or low resistance state, leading to a nonvolatile control of τ_{⊥}/τ_{∥}, consistent with the manipulation of the Rashba SOF strength. Such room temperature electric field control over the spin state is essential for developing energy-efficient spintronic devices and shows promise for complex oxide based (spin) electronics.
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Affiliation(s)
- A M Kamerbeek
- Physics of Nanodevices, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, Netherlands
| | - P Högl
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - J Fabian
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - T Banerjee
- Physics of Nanodevices, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, Netherlands
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49
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Gariglio S, Fête A, Triscone JM. Electron confinement at the LaAlO3/SrTiO3 interface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:283201. [PMID: 26102193 DOI: 10.1088/0953-8984/27/28/283201] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Physical and structural phenomena originating from polar discontinuities have generated enormous activity. In the last ten years, the oxide interface between polar LaAlO(3) and non-polar SrTiO(3), both band insulators, has attracted particular interest, as it hosts an electron liquid with remarkable properties: it superconducts, has a sizeable spin-orbit interaction and its properties are tunable by an electric field. The profile of the carrier density at the interface and the exact band structure are properties strongly linked and still objects of debate. Here we review the experimental findings on the origin and the extension of the electron liquid and discuss the theoretical models developed to describe the charge profile and the band structure. We also introduce a model to account for the effect of interface disorder which could modify the charge distribution.
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Affiliation(s)
- S Gariglio
- DQMP, Université de Genève, 24 Quai E.-Ansermet, CH-1211 Genève, Switzerland
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50
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Boschker H, Richter C, Fillis-Tsirakis E, Schneider CW, Mannhart J. Electron-phonon Coupling and the Superconducting Phase Diagram of the LaAlO3-SrTiO3 Interface. Sci Rep 2015; 5:12309. [PMID: 26169351 PMCID: PMC4648410 DOI: 10.1038/srep12309] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 06/25/2015] [Indexed: 12/03/2022] Open
Abstract
The superconductor at the LaAlO3—SrTiO3 interface provides a model system for the study of two-dimensional superconductivity in the dilute carrier density limit. Here we experimentally address the pairing mechanism in this superconductor. We extract the electron—phonon spectral function from tunneling spectra and conclude, without ruling out contributions of further pairing channels, that electron—phonon mediated pairing is strong enough to account for the superconducting critical temperatures. Furthermore, we discuss the electron—phonon coupling in relation to the superconducting phase diagram. The electron—phonon spectral function is independent of the carrier density, except for a small part of the phase diagram in the underdoped region. The tunneling measurements reveal that the increase of the chemical potential with increasing carrier density levels off and is zero in the overdoped region of the phase diagram. This indicates that the additionally induced carriers do not populate the band that hosts the superconducting state and that the superconducting order parameter therefore is weakened by the presence of charge carriers in another band.
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Affiliation(s)
- Hans Boschker
- Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
| | - Christoph Richter
- 1] Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany [2] Center for Electronic Correlations and Magnetism, Augsburg University, 86135 Augsburg, Germany
| | | | | | - Jochen Mannhart
- Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
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