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Ding C, Dong W, Jiao X, Zhang Z, Gong G, Wei Z, Wang L, Jia JF, Xue QK. Unidirectional Charge Orders Induced by Oxygen Vacancies on SrTiO 3(001). ACS NANO 2024; 18:17786-17793. [PMID: 38935417 DOI: 10.1021/acsnano.4c03317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/28/2024]
Abstract
The discovery of high-mobility two-dimensional electron gas and low carrier density superconductivity in multiple SrTiO3-based heterostructures has stimulated intense interest in the surface properties of SrTiO3. The recent discovery of high-Tc superconductivity in the monolayer FeSe/SrTiO3 led to the upsurge and underscored the atomic precision probe of the surface structure. By performing atomically resolved cryogenic scanning tunneling microscopy/spectroscopy characterization on dual-TiO2-δ-terminated SrTiO3(001) surfaces with (√13 × √13), c(4 × 2), mixed (2 × 1), and (2 × 2) reconstructions, we disclosed universally broken rotational symmetry and contrasting bias- and temperature-dependent electronic states for apical and equatorial oxygen sites. With the sequentially evolved surface reconstructions and simultaneously increasing equatorial oxygen vacancies, the surface anisotropy reduces and the work function lowers. Intriguingly, unidirectional stripe orders appear on the c(4 × 2) surface, whereas local (4 × 4) order emerges and eventually forms long-range unidirectional c(4 × 4) charge order on the (2 × 2) surface. This work reveals robust unidirectional charge orders induced by oxygen vacancies due to strong and delicate electronic-lattice interaction under broken rotational symmetry, providing insights into understanding the complex behaviors in perovskite oxide-based heterostructures.
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Affiliation(s)
- Cui Ding
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Quantum Science Center of Guangdong-HongKong-Macao Greater Bay Area, Shenzhen 518045, China
| | - Wenfeng Dong
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
| | - Xiaotong Jiao
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
| | - Zhiyu Zhang
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
| | - Guanming Gong
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
| | - Zhongxu Wei
- Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China
| | - Lili Wang
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
| | - Jin-Feng Jia
- Quantum Science Center of Guangdong-HongKong-Macao Greater Bay Area, Shenzhen 518045, China
- Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China
- Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Qi-Kun Xue
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Quantum Science Center of Guangdong-HongKong-Macao Greater Bay Area, Shenzhen 518045, China
- Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
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Ritzinger P, Výborný K. Anisotropic magnetoresistance: materials, models and applications. ROYAL SOCIETY OPEN SCIENCE 2023; 10:230564. [PMID: 37859834 PMCID: PMC10582618 DOI: 10.1098/rsos.230564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 09/07/2023] [Indexed: 10/21/2023]
Abstract
Resistance of certain (conductive and otherwise isotropic) ferromagnets turns out to exhibit anisotropy with respect to the direction of magnetization: R ∥ for magnetization parallel to the electric current direction is different from R⊥ for magnetization perpendicular to the electric current direction. In this review, this century-old phenomenon is reviewed both from the perspective of materials and physical mechanisms involved. More recently, this effect has also been identified and studied in antiferromagnets. To date, sensors based on the anisotropic magnetoresistance (AMR) effect are widely used in different fields, such as the automotive industry, aerospace or in biomedical imaging.
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Affiliation(s)
- Philipp Ritzinger
- FZU—Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10, Praha 6 16253, Czech Republic
- MFF—Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, Praha 2 12000, Czech Republic
| | - Karel Výborný
- FZU—Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10, Praha 6 16253, Czech Republic
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3
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Kwon D, Kwak Y, Lee D, Jo W, Cho BG, Koo TY, Song J. Strong Rashba parameter of two-dimensional electron gas at CaZrO 3/SrTiO 3 heterointerface. Sci Rep 2023; 13:15927. [PMID: 37741927 PMCID: PMC10517959 DOI: 10.1038/s41598-023-43247-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Accepted: 09/21/2023] [Indexed: 09/25/2023] Open
Abstract
We synthesized a CaZrO3/SrTiO3 oxide heterostructure, which can serve as an alternative to LaAlO3/SrTiO3, and confirmed the generation of 2-dimensional electron gas (2-DEG) at the heterointerface. We analyzed the electrical-transport properties of the 2-DEG to elucidate its intrinsic characteristics. Based on the magnetic field dependence of resistance at 2 K, which exhibited Weak Anti-localization (WAL) behaviors, the fitted Rashba parameter values were found to be about 12-15 × 10-12 eV*m. These values are stronger than the previous reported Rashba parameters obtained from the 2-DEGs in other heterostructure systems and several layered 2D materials. The observed strong spin-orbit coupling (SOC) is attributed to the strong internal electric field generated by the lattice mismatch between the CaZrO3 layer and SrTiO3 substrate. This pioneering strong SOC of the 2-DEG at the CaZrO3/SrTiO3 heterointerface may play a pivotal role in the developing future metal oxide-based quantum nanoelectronics devices.
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Affiliation(s)
- Duhyuk Kwon
- Department of Physics, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Yongsu Kwak
- Department of Physics, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Doopyo Lee
- Department of Physics, Pohang University of Science and Technology, Pohang, Gyeongbuk, 37673, Republic of Korea
| | - Wonkeun Jo
- The Division of Computer Convergence, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Byeong-Gwan Cho
- Pohang Accelerator Laboratory, Pohang, Gyeongbuk, 37673, Republic of Korea
| | - Tae-Yeong Koo
- Pohang Accelerator Laboratory, Pohang, Gyeongbuk, 37673, Republic of Korea
| | - Jonghyun Song
- Department of Physics, Chungnam National University, Daejeon, 34134, Republic of Korea.
- Institute of Quantum Systems (IQS), Chungnam National University, Daejeon, 34134, Republic of Korea.
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Extremely low-energy ARPES of quantum well states in cubic-GaN/AlN and GaAs/AlGaAs heterostructures. Sci Rep 2021; 11:19081. [PMID: 34580361 PMCID: PMC8476498 DOI: 10.1038/s41598-021-98569-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Accepted: 08/25/2021] [Indexed: 11/30/2022] Open
Abstract
Quantum well (QW) heterostructures have been extensively used for the realization of a wide range of optical and electronic devices. Exploiting their potential for further improvement and development requires a fundamental understanding of their electronic structure. So far, the most commonly used experimental techniques for this purpose have been all-optical spectroscopy methods that, however, are generally averaging in momentum space. Additional information can be gained by angle-resolved photoelectron spectroscopy (ARPES), which measures the electronic structure with momentum resolution. Here we report on the use of extremely low-energy ARPES (photon energy ~ 7 eV) to increase depth sensitivity and access buried QW states, located at 3 nm and 6 nm below the surface of cubic-GaN/AlN and GaAs/AlGaAs heterostructures, respectively. We find that the QW states in cubic-GaN/AlN can indeed be observed, but not their energy dispersion, because of the high surface roughness. The GaAs/AlGaAs QW states, on the other hand, are buried too deep to be detected by extremely low-energy ARPES. Since the sample surface is much flatter, the ARPES spectra of the GaAs/AlGaAs show distinct features in momentum space, which can be reconducted to the band structure of the topmost surface layer of the QW structure. Our results provide important information about the samples’ properties required to perform extremely low-energy ARPES experiments on electronic states buried in semiconductor heterostructures.
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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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Li M, Zhou Y, Chen Y, Yang R, Wei X, Wang S, Jin K. Effect of Rare Earth Elements at Amorphous ReAlO 3/SrTiO 3 (Re = La, Pr, Nd, Sm, Gd, and Tm) Heterointerfaces. J Phys Chem Lett 2021; 12:1657-1663. [PMID: 33555878 DOI: 10.1021/acs.jpclett.0c03685] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Although the amorphous two-dimensional electron gas (a-2DEG) of oxides provides new opportunities to explore nanoelectronic as well as quantum devices, the intrinsic effect of rare earth (Re = La, Pr, Nd, Sm, Gd, and Tm) elements at ReAlO3/SrTiO3 heterointerfaces is still largely unknown and needs to be addressed systematically. Herein, we first propose that the ionization potential of Re elements is a critical factor for the 2DEG fabricated by chemical spin coating. Furthermore, the photoresponsive properties of heterointerfaces are investigated comprehensively with the ionization potential ranging from 35.79 to 41.69 eV. The results show that the sheet resistances significantly increase with increasing the ionization potential, and a resistance upturn phenomenon is observed at TmAlO3/SrTiO3 heterointerfaces, which can be attributed to the weak localization effect theoretically. The most important observation is the dramatic transition from negative (-178.3%, Re = La) to positive (+89.9%, Re = Gd) photoresponse at ReAlO3/SrTiO3 heterointerfaces under the irradiation of 405 nm light at 50 K. More remarkably, a unique recovery behavior of transient-persistent photoconductivity coexistence at low temperatures is discovered at the TmAlO3/SrTiO3 heterointerface. This work reveals an effective approach to tune the transport and photoresponsive properties by changing Re elements and paves the way for the application of all-oxide devices.
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Affiliation(s)
- Ming Li
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - You Zhou
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - Yunhai Chen
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - Ruishu Yang
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - Xiangyang Wei
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - Shuanhu Wang
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - Kexin Jin
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
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Chen X, Zhang T, Yu Y, Cai X, Gao T, Zhang T, Sun H, Gu C, Gu Z, Zhu Y, Zhou J, Nie Y, Pan X. Rewritable High-Mobility Electrons in Oxide Heterostructure of Layered Perovskite/Perovskite. ACS APPLIED MATERIALS & INTERFACES 2021; 13:7812-7821. [PMID: 33529011 DOI: 10.1021/acsami.1c00481] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Perovskite oxide SrTiO3 can be electron-doped and exhibits high mobility by introducing oxygen vacancies or dopants such as Nb or La. A reversible after-growth tuning of high mobility carriers in SrTiO3 is highly desired for the applications in high-speed electronic devices. Here, we report the observation of tunable high-mobility electrons in layered perovskite/perovskite (Srn+1TinO3n+1/SrTiO3) heterostructure. By use of Srn+1TinO3n+1 as the oxygen diffusion barrier, the oxygen vacancy concentration near the interface can be reversibly engineered by high-temperature annealing or infrared laser heating. Because of the identical elemental compositions (Sr, Ti, and O) throughout the whole heterostructure, interfacial ionic intermixing is absent, giving rise to an extremely high mobility (exceeding 55000 cm2 V-1 s-1 at 2 K) in this type of oxide heterostructure. This layered perovskite/perovskite heterostructure provides a promising platform for reconfigurable high-speed electronic devices.
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Affiliation(s)
- Xiaofeng Chen
- National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Tingting Zhang
- National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Yang Yu
- National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Xiangbin Cai
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
| | - Tianyi Gao
- National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Tianwei Zhang
- National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Haoying Sun
- National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Chenyi Gu
- National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Zhengbin Gu
- National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Ye Zhu
- Department of Applied Physics, Research Institute for Smart Energy, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
| | - Jian Zhou
- National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Yuefeng Nie
- National Laboratory of Solid State Microstructures, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Xiaoqing Pan
- Department of Materials Science and Engineering, Department of Physics and Astronomy, University of California, Irvine, Irvine, California 92697, United States
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He R, Lin JL, Liu Q, Liao Z, Shui L, Wang ZJ, Zhong Z, Li RW. Emergent Ferroelectricity in Otherwise Nonferroelectric Oxides by Oxygen Vacancy Design at Heterointerfaces. ACS APPLIED MATERIALS & INTERFACES 2020; 12:45602-45610. [PMID: 32929952 DOI: 10.1021/acsami.0c13314] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Introducing point defects in complex metal oxides is a very effective route to engineer crystal symmetry and therefore control physical properties. However, the inversion symmetry breaking, which is vital for many tantalizing properties, such as ferroelectricity and chiral spin structure, is usually hard to be induced in the bulk crystal by point defects. By designing the oxygen vacancy formation energy profile and migration path across the oxide heterostructure, our first-principles density functional theory (DFT) calculations demonstrate that the point defects can effectively break the inversion symmetry and hence create novel ferroelectricity in superlattices consisting of otherwise nonferroelectric materials SrTiO3 and SrRuO3. This induced ferroelectricity can be significantly enhanced by reducing the SrTiO3 thickness. Inspired by theory calculation, SrTiO3/SrRuO3 superlattices were experimentally fabricated and are found to exhibit surprising strong ferroelectric properties. Our finding paves a simple and effective pathway to engineer the inversion symmetry and thus properties by point defect control in oxide heterostructures.
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Affiliation(s)
- Ri He
- Key Laboratory of Magnetic Materials Devices & Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
- School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006, China
- International Academy of Optoelectronics at Zhaoqing, South China Normal University, Zhaoqing 526238, China
| | - Jun Liang Lin
- College of Light Industry, Liaoning University, Shenyang 110036, China
- School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
| | - Qing Liu
- Key Laboratory of Magnetic Materials Devices & Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
| | - Zhaoliang Liao
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230026, China
| | - Lingling Shui
- School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006, China
| | - Zhan Jie Wang
- School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870, China
| | - Zhicheng Zhong
- Key Laboratory of Magnetic Materials Devices & Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
- China Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Run-Wei Li
- Key Laboratory of Magnetic Materials Devices & Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
- China Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
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Briceño RCB, Fernández VI, Alonso RE. First-principles study of the ferroelectric properties of SrTaO 2N/SrTiO 3interfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:355003. [PMID: 32203943 DOI: 10.1088/1361-648x/ab8251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 03/23/2020] [Indexed: 06/10/2023]
Abstract
First-principles calculations based on density-functional theory in the pseudo-potential approach have been performed for the total energy, crystal structure and cell polarization for SrTaO2N/SrTiO3heterostructures. Different heterojunctions were analyzed in terms of the termination atoms at the interface plane, and periodic or non-periodic stacking in the perpendicular direction. The calculations show that the SrTaO2N layer is compressed along theab-plane, while the SrTiO3is elongated, thus favoring the formation ofP4mmlocal environment on both sides of the interface, leading to net macroscopic polarization. The analysis of the local polarization as a function of the distance to the interface, for each individual unit cell was found to depend on the presence of a N or an O atom at the interface, and also on the asymmetric and not uniformc-axis deformation due to the induced strain in theab-plane. The resulting total polarization in the periodic array was ≈0.54 C m-2, which makes this type of arrangement suitable for microelectronic applications.
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Affiliation(s)
- R C Bastidas Briceño
- Departamento de Ciencias Básicas, Facultad de Ingeniería Universidad Nacional de La Plata, La Plata, Argentina
- Instituto de Física La Plata (IFLP), CONICET, Argentina
| | - V I Fernández
- Instituto de Física La Plata (IFLP), CONICET, Argentina
- Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina
| | - R E Alonso
- Departamento de Ciencias Básicas, Facultad de Ingeniería Universidad Nacional de La Plata, La Plata, Argentina
- Instituto de Física La Plata (IFLP), CONICET, Argentina
- Instituto de Ingeniería y Agronomía, Universidad Nacional Arturo Jauretche, Argentina
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10
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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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11
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Wadehra N, Tomar R, Varma RM, Gopal RK, Singh Y, Dattagupta S, Chakraverty S. Planar Hall effect and anisotropic magnetoresistance in polar-polar interface of LaVO 3-KTaO 3 with strong spin-orbit coupling. Nat Commun 2020; 11:874. [PMID: 32054860 PMCID: PMC7018836 DOI: 10.1038/s41467-020-14689-z] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Accepted: 01/23/2020] [Indexed: 11/26/2022] Open
Abstract
Among the perovskite oxide family, KTaO3 (KTO) has recently attracted considerable interest as a possible system for the realization of the Rashba effect. In this work, we report a novel conducting interface by placing KTO with another insulator, LaVO3 (LVO) and report planar Hall effect (PHE) and anisotropic magnetoresistance (AMR) measurements. This interface exhibits a signature of strong spin-orbit coupling. Our experimental observations of two fold AMR and PHE at low magnetic fields (B) is similar to those obtained for topological systems and can be intuitively understood using a phenomenological theory for a Rashba spin-split system. Our experimental data show a B2 dependence of AMR and PHE at low magnetic fields that could also be explained based on our model. At high fields (~8 T), we see a two fold to four fold transition in the AMR that could not be explained using only Rashba spin-split energy spectra. Two dimensional electron gas (2DEG) at oxide interfaces is promising in modern electronic devices. Here, Wadehra et al. realize 2DEG at a novel interface composed of LaVO3 and KTaO3, where strong spin-orbit coupling and relativistic nature of the electrons in the 2DEG, leading to anisotropic magnetoresistance and planar Hall effect.
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Affiliation(s)
- Neha Wadehra
- Nanoscale Physics and Device Laboratory, Institute of Nano Science and Technology, Phase-10, Sector-64, Mohali, Punjab, 160062, India
| | - Ruchi Tomar
- Nanoscale Physics and Device Laboratory, Institute of Nano Science and Technology, Phase-10, Sector-64, Mohali, Punjab, 160062, India
| | - Rahul Mahavir Varma
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangaluru, Karnataka, 560012, India
| | - R K Gopal
- Indian Institute of Science Education and Research Mohali, Knowledge City, Sector-81, SAS Nagar, Manauli, 140306, India
| | - Yogesh Singh
- Indian Institute of Science Education and Research Mohali, Knowledge City, Sector-81, SAS Nagar, Manauli, 140306, India
| | - Sushanta Dattagupta
- Bose Institute, P-1/12, CIT Rd, Scheme VIIM, Kankurgachi, Kolkata, West Bengal, 700054, India
| | - S Chakraverty
- Nanoscale Physics and Device Laboratory, Institute of Nano Science and Technology, Phase-10, Sector-64, Mohali, Punjab, 160062, India.
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Interface polarization model for a 2-dimensional electron gas at the BaSnO 3/LaInO 3 interface. Sci Rep 2019; 9:16202. [PMID: 31700133 PMCID: PMC6838460 DOI: 10.1038/s41598-019-52772-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Accepted: 10/22/2019] [Indexed: 11/23/2022] Open
Abstract
In order to explain the experimental sheet carrier density n2D at the interface of BaSnO3/LaInO3, we consider a model that is based on the presence of interface polarization in LaInO3 which extends over 2 pseudocubic unit cells from the interface and eventually disappears in the next 2 unit cells. Considering such interface polarization in calculations based on 1D Poisson-Schrödinger equations, we consistently explain the dependence of the sheet carrier density of BaSnO3/LaInO3 heterinterfaces on the thickness of the LaInO3 layer and the La doping of the BaSnO3 layer. Our model is supported by a quantitative analysis of atomic position obtained from high resolution transmission electron microscopy which evidences suppression of the octahedral tilt and a vertical lattice expansion in LaInO3 over 2–3 pseudocubic unit cells at the coherently strained interface.
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13
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Li G, Huang H, Peng S, Xiong Y, Xiao Y, Yan S, Cao Y, Tang M, Li Z. Two-dimensional polar metals in KNbO 3/BaTiO 3 superlattices: first-principle calculations. RSC Adv 2019; 9:35499-35508. [PMID: 35528067 PMCID: PMC9074721 DOI: 10.1039/c9ra06209b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Accepted: 10/25/2019] [Indexed: 11/21/2022] Open
Abstract
Polar metals, commonly defined by the coexistence of polar structure and metallicity, are thought to be scarce because free carriers eliminate internal dipoles that may arise owing to asymmetric charge distributions. By using first-principle electronic structure calculations, we explored the possibility of producing metallic states in the polar/nonpolar KNbO3/BaTiO3 superlattice (SL) composed of two prototypical ferroelectric materials: BaTiO3 (BTO) and KNbO3 (KNO). Two types of polar/nonpolar interfaces, p-type (KO)−/(TiO2)0 and n-type (NbO2)+/(BaO)0, which can be constituted into two symmetric NbO2/BaO–NbO2/BaO (NN-type) and KO/TiO2–KO/TiO2 (PP-type) SL, as well as one asymmetric KO/TiO2–NbO2/BaO (PN-type) SL. The spatial distribution of ferroelectric distortions and their conductive properties are found to be extraordinarily sensitive to the interfacial configurations. An insulator-to-metal transition is found in each unit cell of the symmetric interfacial SL models: one exhibiting quasi-two-dimensional n-type conductivity for NN-type SL, while the other being quasi-two-dimensional p-type conductivity for PP-type SL. The anisotropic coexistence of in-plane orientation of free carriers and out-of-plane orientation of ferroelectric polarization in KNO/BTO SL indicates that in-plane free carriers can not eliminate the out-of-plane dipoles. Our results provide a road map to create two-dimensional polar metals in insulating perovskite oxide SL, which is expected to promote applications of new quantum devices. Polar metals, commonly defined by the coexistence of polar structure and metallicity, are thought to be scarce because free carriers eliminate internal dipoles that may arise owing to asymmetric charge distributions.![]()
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Affiliation(s)
- Gang Li
- School of Materials Science and Engineering, Xiangtan University Xiangtan Hunan 411105 China
| | - Huiyu Huang
- School of Materials Science and Engineering, Xiangtan University Xiangtan Hunan 411105 China
| | - Shaoqin Peng
- School of Materials Science and Engineering, Xiangtan University Xiangtan Hunan 411105 China
| | - Ying Xiong
- School of Mathematics and Computational Science, Xiangtan University Xiangtan 411105 China
| | - Yongguang Xiao
- School of Materials Science and Engineering, Xiangtan University Xiangtan Hunan 411105 China
| | - Shaoan Yan
- School of Mechanical Engineering, Xiangtan University Xiangtan 411105 China
| | - Yanwei Cao
- CAS Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences Ningbo Zhejiang 315201 China
| | - Minghua Tang
- School of Materials Science and Engineering, Xiangtan University Xiangtan Hunan 411105 China
| | - Zheng Li
- School of Materials Science and Engineering, Xiangtan University Xiangtan Hunan 411105 China
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Dai W, Liang Y, Yang M, Schrecongost D, Gajurel P, Lee H, Lee JW, Chen J, Eom CB, Cen C. Large and Reconfigurable Infrared Photothermoelectric Effect at Oxide Interfaces. NANO LETTERS 2019; 19:7149-7154. [PMID: 31525937 DOI: 10.1021/acs.nanolett.9b02712] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
To maximize the photovoltaic efficiency, it is highly desirable to enable the electricity conversion from low energy photons and to extract the excessive energy from hot carriers. Here we report a large photovoltage generation at the LaAlO3/SrTiO3 interfaces from infrared photons with energies far below the oxide bandgaps. This effect is a result of the photoexcitation of hot carriers in metasurface electrical contacts and the subsequent thermoelectric charge separations by the interfacial two-dimensional electron gas (2DEG). Reaching a room-temperature responsivity of 4.4 V/W, such light-to-charge conversion can be spatially controlled and reconfigured through the patterning of 2DEG using conducting atomic force microscope. Compatible for broadband applications, our results demonstrate a new path toward efficient and programmable light sensing using oxide-based low-dimensional electron systems.
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Affiliation(s)
- Weitao Dai
- Department of Physics and Astronomy , West Virginia University , Morgantown , West Virginia 26506 , United States
| | - Yi Liang
- Department of Physics and Astronomy , West Virginia University , Morgantown , West Virginia 26506 , United States
- Guangxi Key Lab for Relativistic Astrophysics, Center on Nanoenergy Research, School of Physical Science and Technology , Guangxi University, Nanning , Guangxi 530004 , China
| | - Ming Yang
- Department of Physics and Astronomy , West Virginia University , Morgantown , West Virginia 26506 , United States
| | - Dustin Schrecongost
- Department of Physics and Astronomy , West Virginia University , Morgantown , West Virginia 26506 , United States
| | - Prakash Gajurel
- 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
| | - Jun Chen
- Department of Electrical and Computer Engineering and Peterson Institute of NanoScience and Engineering , University of Pittsburgh , Pittsburgh , Pennsylvania 15261 , 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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15
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A termination-insensitive and robust electron gas at the heterointerface of two complex oxides. Nat Commun 2019; 10:4026. [PMID: 31492862 PMCID: PMC6731279 DOI: 10.1038/s41467-019-12036-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Accepted: 08/13/2019] [Indexed: 11/29/2022] Open
Abstract
The single-crystal SrTiO3 (001) has two different surface terminations, TiO2 and SrO. One most remarkable observation in previous studies is that only the heterointerfaces with TiO2-terminated SrTiO3, which usually combines with polar oxides such as LaAlO3, host an electron gas. Here we show that a robust electron gas can be generated between a non-polar oxide, CaHfO3, and SrTiO3 (001) with either termination. Unlike the well-known electron gas of LaAlO3/SrTiO3, the present one of CaHfO3/SrTiO3 essentially has no critical thickness of CaHfO3, can survive a long-time oxygen annealing at high temperature, and its transport properties are stable under exposure to water and other polar solvents. By electrostatic gating through CaHfO3, field-effect devices are demonstrated using CaHfO3/SrTiO3 heterointerfaces with both terminations. These results show that the electron gas reported in the present study is unique and promising for applications in oxide electronics. Two dimensional electron gases (EG) at the heterointerface of complex oxides show fascinating properties. The authors report on an EG formed at the CaHfO3/SrTiO3 interface independent of interface termination and robust against environmental conditions most likely originating from oxygen non-stoichiometry.
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16
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Dos Santos-Gómez L, Sanna S, Norby P, Pryds N, Losilla ER, Marrero-López D, Esposito V. Electrochemical stability of (La,Sr)CoO 3-δ in (La,Sr)CoO 3-δ/(Ce, Gd)O 2-δ heterostructures. NANOSCALE 2019; 11:2916-2924. [PMID: 30688947 DOI: 10.1039/c8nr08528e] [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
A modulated coherent (La,Sr)CoO3-δ/(Ce,Gd)O2-δ heterostructure is characterized for the first time for its electronic and chemical properties. 2D-multilayer architectures are deposited on NdGaO3 (110) single crystal substrate by pulsed laser deposition, resulting in epitaxial structures with in-plane lattice rotation that, via the metal oxides' interfaces, induces mutual structural rearrangements. Our results show that (La,Sr)CoO3-d thin films of 10-100 nm are chemically unstable when exposed to air at 600 °C during electrical cyclic stress-tests. Conversely, improved stability is achieved confining LSC in the nanometric heterostructure. Remarkably, the chemical stabilization occurs without compromising substantially the electrical properties of the LSC component: the heterostructures show unexpected electrical behaviour with dominant electronic contributions, fast conductivity and mixed ionic-electronic properties, depending on the number of interfaces and the nano-scaled layers.
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Affiliation(s)
- Lucía Dos Santos-Gómez
- Department of Energy Conversion and Storage, Technical University of Denmark, DTU Risø Campus, DK-4000 Roskilde, Denmark.
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17
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Zhang Y, Lu H, Xie L, Yan X, Paudel TR, Kim J, Cheng X, Wang H, Heikes C, Li L, Xu M, Schlom DG, Chen LQ, Wu R, Tsymbal EY, Gruverman A, Pan X. Anisotropic polarization-induced conductance at a ferroelectric-insulator interface. NATURE NANOTECHNOLOGY 2018; 13:1132-1136. [PMID: 30250247 DOI: 10.1038/s41565-018-0259-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Accepted: 08/16/2018] [Indexed: 05/12/2023]
Abstract
Coupling between different degrees of freedom, that is, charge, spin, orbital and lattice, is responsible for emergent phenomena in complex oxide heterostrutures1,2. One example is the formation of a two-dimensional electron gas (2DEG) at the polar/non-polar LaAlO3/SrTiO3 (LAO/STO)3-7 interface. This is caused by the polar discontinuity and counteracts the electrostatic potential build-up across the LAO film3. The ferroelectric polarization at a ferroelectric/insulator interface can also give rise to a polar discontinuity8-10. Depending on the polarization orientation, either electrons or holes are transferred to the interface, to form either a 2DEG or two-dimensional hole gas (2DHG)11-13. While recent first-principles modelling predicts the formation of 2DEGs at the ferroelectric/insulator interfaces9,10,12-14, experimental evidence of a ferroelectrically induced interfacial 2DEG remains elusive. Here, we report the emergence of strongly anisotropic polarization-induced conductivity at a ferroelectric/insulator interface, which shows a strong dependence on the polarization orientation. By probing the local conductance and ferroelectric polarization over a cross-section of a BiFeO3-TbScO3 (BFO/TSO) (001) heterostructure, we demonstrate that this interface is conducting along the 109° domain stripes in BFO, whereas it is insulating in the direction perpendicular to these domain stripes. Electron energy-loss spectroscopy and theoretical modelling suggest that the anisotropy of the interfacial conduction is caused by an alternating polarization associated with the ferroelectric domains, producing either electron or hole doping of the BFO/TSO interface.
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Affiliation(s)
- Yi Zhang
- Department of Materials Science and Engineering, University of California, Irvine, CA, USA
| | - Haidong Lu
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA
| | - Lin Xie
- National Laboratory of Solid State Microstructures and College of Engineering and Applied Sciences, Nanjing University, Nanjing, Jiangsu, China
| | - Xingxu Yan
- Department of Materials Science and Engineering, University of California, Irvine, CA, USA
| | - Tula R Paudel
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA
| | - Jeongwoo Kim
- Department of Physics and Astronomy, University of California, Irvine, CA, USA
| | - Xiaoxing Cheng
- Department of Materials Science and Engineering, Penn State University, University Park, PA, USA
| | - Hui Wang
- Department of Physics and Astronomy, University of California, Irvine, CA, USA
| | - Colin Heikes
- Department of Materials Science and Engineering, Cornell University, Ithaca, NY, USA
| | - Linze Li
- Department of Materials Science and Engineering, University of California, Irvine, CA, USA
| | - Mingjie Xu
- Department of Materials Science and Engineering, University of California, Irvine, CA, USA
| | - Darrell G Schlom
- Department of Materials Science and Engineering, Cornell University, Ithaca, NY, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA
| | - Long-Qing Chen
- Department of Materials Science and Engineering, Penn State University, University Park, PA, USA
| | - Ruqian Wu
- Department of Physics and Astronomy, University of California, Irvine, CA, USA
| | - Evgeny Y Tsymbal
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA
| | - Alexei Gruverman
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, USA.
| | - Xiaoqing Pan
- Department of Materials Science and Engineering, University of California, Irvine, CA, USA.
- Department of Physics and Astronomy, University of California, Irvine, CA, USA.
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18
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k-space imaging of anisotropic 2D electron gas in GaN/GaAlN high-electron-mobility transistor heterostructures. Nat Commun 2018; 9:2653. [PMID: 29992961 PMCID: PMC6041315 DOI: 10.1038/s41467-018-04354-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Accepted: 04/09/2018] [Indexed: 11/29/2022] Open
Abstract
Nanostructures based on buried interfaces and heterostructures are at the heart of modern semiconductor electronics as well as future devices utilizing spintronics, multiferroics, topological effects, and other novel operational principles. Knowledge of electronic structure of these systems resolved in electron momentum k delivers unprecedented insights into their physics. Here we explore 2D electron gas formed in GaN/AlGaN high-electron-mobility transistor heterostructures with an ultrathin barrier layer, key elements in current high-frequency and high-power electronics. Its electronic structure is accessed with angle-resolved photoelectron spectroscopy whose probing depth is pushed to a few nanometers using soft-X-ray synchrotron radiation. The experiment yields direct k-space images of the electronic structure fundamentals of this system—the Fermi surface, band dispersions and occupancy, and the Fourier composition of wavefunctions encoded in the k-dependent photoemission intensity. We discover significant planar anisotropy of the electron Fermi surface and effective mass connected with relaxation of the interfacial atomic positions, which translates into nonlinear (high-field) transport properties of the GaN/AlGaN heterostructures as an anisotropy of the saturation drift velocity of the 2D electrons. Semiconductor heterostructures hosting two-dimensional electron gases are widely used today in high-electron-mobility transistors. Here, the authors probe the electronic structure in GaN/AlGaN, heterostructures, discovering planar anisotropy of the electron Fermi surface, offering new insights into transport properties.
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19
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Chen L, Li J, Tang Y, Pai YY, Chen Y, Pryds N, Irvin P, Levy J. Extreme Reconfigurable Nanoelectronics at the CaZrO 3 /SrTiO 3 Interface. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1801794. [PMID: 29962024 DOI: 10.1002/adma.201801794] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Revised: 05/10/2018] [Indexed: 06/08/2023]
Abstract
Complex oxide heterostructures have fascinating emergent properties that originate from the properties of the bulk constituents as well as from dimensional confinement. The conductive behavior of the polar/nonpolar LaAlO3 /SrTiO3 interface can be reversibly switched using conductive atomic force microscopy (c-AFM) lithography, enabling a wide range of devices and physics to be explored. Here, extreme nanoscale control over the CaZrO3 /SrTiO3 (CZO/STO) interface, which is formed from two materials that are both nonpolar, is reported. Nanowires with measured widths as narrow as 1.2 nm are realized at the CZO/STO interface at room temperature by c-AFM lithography. These ultrathin nanostructures have spatial dimensions at room temperature that are comparable to single-walled carbon nanotubes, and hold great promise for alternative oxide-based nanoelectronics, as well as offer new opportunities to investigate the electronic structure of the complex oxide interfaces. The cryogenic properties of devices constructed from quasi-1D channels, tunnel barriers, and planar gates exhibit gate-tunable superconductivity, quantum oscillations, electron pairing outside of the superconducting regime, and quasi-ballistic transport. This newly demonstrated ability to control the metal-insulator transition at nonpolar oxide interface greatly expands the class of materials whose behavior can be patterned and reconfigured at extreme nanoscale dimensions.
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Affiliation(s)
- Lu Chen
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, 15260, USA
- Pittsburgh Quantum Institute, Pittsburgh, PA, 15260, USA
| | - Jianan Li
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, 15260, USA
- Pittsburgh Quantum Institute, Pittsburgh, PA, 15260, USA
| | - Yuhe Tang
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, 15260, USA
- Pittsburgh Quantum Institute, Pittsburgh, PA, 15260, USA
| | - Yun-Yi Pai
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, 15260, USA
- Pittsburgh Quantum Institute, Pittsburgh, PA, 15260, USA
| | - Yunzhong Chen
- Department of Energy Conversion and Storage, Technical University of Denmark, Risø Campus, Roskilde, 4000, Denmark
| | - Nini Pryds
- Department of Energy Conversion and Storage, Technical University of Denmark, Risø Campus, Roskilde, 4000, Denmark
| | - Patrick Irvin
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, 15260, USA
- Pittsburgh Quantum Institute, Pittsburgh, PA, 15260, USA
| | - Jeremy Levy
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, 15260, USA
- Pittsburgh Quantum Institute, Pittsburgh, PA, 15260, USA
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20
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Lu Y, Wang F, Chen M, Lan Z, Ren Z, Tian H, Yang K. Tuning Interfacial Magnetic Ordering via Polarization Control in Ferroelectric SrTiO 3/PbTiO 3 Heterostructure. ACS APPLIED MATERIALS & INTERFACES 2018; 10:10536-10542. [PMID: 29481040 DOI: 10.1021/acsami.7b19112] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The electromagnetic properties at the interface of heterostructure are sensitive to the interfacial crystal structure and external field. For example, the two-dimensional magnetic states at the interface of LaAlO3/SrTiO3 are discovered and can further be controlled by electric field. Here, we study two types of heterostructures, TiO2/PbTiO3 and SrTiO3/PbTiO3, using first-principle electronic structure calculations. We find that the ferroelectric polarization discontinuity at the interface leads to partially occupied Ti 3d states and the magnetic moments. The magnitude of the magnetic moments and the ground-state magnetic coupling are sensitive to the polarization intensity of PbTiO3. As the ferroelectric polarization of PbTiO3 increases, the two heterostructures show different magnetic ordering that strongly depends on the electron occupation of the Ti t2g orbitals. For the TiO2/PbTiO3 interface, the magnetic moments are mostly contributed by degenerated d yz/d xz orbitals of interfacial Ti atoms and the neighboring interfacial Ti atoms form ferromagnetic coupling. For SrTiO3/PbTiO3 interface, the interfacial magnetic moments are mainly contributed by occupied d xy orbital because of the increased polarization intensity, and as the electron occupation increases, there exists a transition of the magnetic coupling between neighboring Ti atoms from ferromagnetism to antiferromagnetism via the superexchange interaction. Our study suggests that manipulating the polarization intensity is one effective way to control interfacial magnetic ordering in the perovskite oxide heterostructures.
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Affiliation(s)
- Yunhao Lu
- School of Materials Science and Engineering , Zhejiang University , Hangzhou 310027 , China
| | - Fang Wang
- School of Materials Science and Engineering , Zhejiang University , Hangzhou 310027 , China
| | - Miaogen Chen
- Department of Physics , China Jiliang University , Hangzhou 310018 , China
| | - Zhenyun Lan
- School of Materials Science and Engineering , Zhejiang University , Hangzhou 310027 , China
| | - Zhaohui Ren
- School of Materials Science and Engineering , Zhejiang University , Hangzhou 310027 , China
| | - He Tian
- School of Materials Science and Engineering , Zhejiang University , Hangzhou 310027 , China
| | - Kesong Yang
- Department of NanoEngineering , University of California San Diego , 9500 Gilman Drive , Mail Code 0448, La Jolla, San Diego , California 92093-0448 , United States
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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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22
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Thickness Control of the Spin-Polarized Two-Dimensional Electron Gas in LaAlO 3/BaTiO 3 Superlattices. Sci Rep 2018; 8:467. [PMID: 29323182 PMCID: PMC5765129 DOI: 10.1038/s41598-017-18858-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2017] [Accepted: 12/18/2017] [Indexed: 11/08/2022] Open
Abstract
We explored the possibility of increasing the interfacial carrier quantum confinement, mobility and conductivity in the (LaAlO3)n/(BaTiO3)n superlattices by thickness regulation using the first-principles electronic structure calculations. Through constructing two different interfacial types of LaAlO3/BaTiO3 superlattices, we discovered that the LaO/TiO2 interface is preferred from cleavage energy consideration. We then studied the electronic characteristics of two-dimensional electron gas (2DEG) produced at the LaO/TiO2 interface in the LaAlO3/BaTiO3 superlattices via spin-polarized density functional theory calculations. The charge carrier density of 2DEG has a magnitude of 1014 cm−2 (larger than the traditional system LaAlO3/SrTiO3), which is mainly provided by the interfacial Ti 3dxy orbitals when the thicknesses of LaAlO3 and BaTiO3 layers are over 4.5 unit cells. We have also revealed the interfacial electronic characteristics of the LaAlO3/BaTiO3 system, by showing the completely spin-polarized 2DEG mostly confined at the superlattice interface. The interfacial charge carrier mobility and conductivity are found to be converged beyond the critical thickness. Therefore, we can regulate the interfacial confinement for the spin-polarized 2DEG and quantum transport properties in LaAlO3/BaTiO3 superlattice via controlling the thicknesses of the LaAlO3 and BaTiO3 layers.
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Zhang Y, Gan Y, Niu W, Norrman K, Yan X, Christensen DV, von Soosten M, Zhang H, Shen B, Pryds N, Sun J, Chen Y. Tuning the Two-Dimensional Electron Gas at Oxide Interfaces with Ti-O Configurations: Evidence from X-ray Photoelectron Spectroscopy. ACS APPLIED MATERIALS & INTERFACES 2018; 10:1434-1439. [PMID: 29226677 DOI: 10.1021/acsami.7b16510] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A chemical redox reaction can lead to a two-dimensional electron gas at the interface between a TiO2-terminated SrTiO3 (STO) substrate and an amorphous LaAlO3 capping layer. When replacing the STO substrate with rutile and anatase TiO2 substrates, considerable differences in the interfacial conduction are observed. On the basis of X-ray photoelectron spectroscopy (XPS) and transport measurements, we conclude that the interfacial conduction comes from redox reactions, and that the differences among the materials systems result mainly from variations in the activation energies for the diffusion of oxygen vacancies at substrate surfaces.
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Affiliation(s)
- Yu Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, People's Republic of China
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - Yulin Gan
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - Wei Niu
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - Kion Norrman
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - Xi Yan
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, People's Republic of China
| | - Dennis Valbjørn Christensen
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - Merlin von Soosten
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - Hongrui Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, People's Republic of China
| | - Baogen Shen
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, People's Republic of China
| | - Nini Pryds
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - Jirong Sun
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, People's Republic of China
| | - Yunzhong Chen
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
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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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25
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Zhang H, Zhang H, Yan X, Zhang X, Zhang Q, Zhang J, Han F, Gu L, Liu B, Chen Y, Shen B, Sun J. Highly Mobile Two-Dimensional Electron Gases with a Strong Gating Effect at the Amorphous LaAlO 3/KTaO 3 Interface. ACS APPLIED MATERIALS & INTERFACES 2017; 9:36456-36461. [PMID: 28972361 DOI: 10.1021/acsami.7b12814] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Two-dimensional electron gas (2DEG) at the perovskite oxide interface exhibits a lot of exotic properties, presenting a promising platform for the exploration of emergent phenomena. While most of the previous works focused on SrTiO3-based 2DEG, here we report on the fabrication of high-quality 2DEGs by growing an amorphous LaAlO3 layer on a (001)-orientated KTaO3 substrate, which is a 5d metal oxide with a polar surface, at a high temperature that is usually adopted for crystalline LaAlO3. Metallic 2DEGs with a Hall mobility as high as ∼2150 cm2/(V s) and a sheet carrier density as low as 2 × 1012 cm-2 are obtained. For the first time, the gating effect on the transport process is studied, and its influence on spin relaxation and inelastic and elastic scattering is determined. Remarkably, the spin relaxation time can be strongly tuned by a back gate. It is reduced by a factor of ∼69 while the gate voltage is swept from -25 to +100 V. The mechanism that dominates the spin relaxation is elucidated.
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Affiliation(s)
- Hui Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Hongrui Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Xi Yan
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Xuejing Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Qinghua Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Jing Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Furong Han
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Lin Gu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Banggui Liu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Yuansha Chen
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Baogen Shen
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
| | - Jirong Sun
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, Peoples' Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences , Beijing 100049, Peoples' Republic of China
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26
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Eom K, Choi E, Yoon J, Choi M, Song K, Choi SY, Lee D, Lee JW, Eom CB, Lee J. Electron-Lattice Coupling in Correlated Materials of Low Electron Occupancy. NANO LETTERS 2017; 17:5458-5463. [PMID: 28850246 DOI: 10.1021/acs.nanolett.7b02109] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In correlated materials including transition metal oxides, electronic properties and functionalities are modulated and enriched by couplings between the electron and lattice degrees of freedom. These couplings are controlled by external parameters such as chemical doping, pressure, magnetic and electric fields, and light irradiation. However, the electron-lattice coupling relies on orbital characters, i.e., symmetry and occupancy, of t2g and eg orbitals, so that a large electron-lattice coupling is limited to eg electron system, whereas t2g electron system exhibits an inherently weak coupling. Here, we design and demonstrate a strongly enhanced electron-lattice coupling in electron-doped SrTiO3, that is, the t2g electron system. In ultrathin films of electron-doped SrTiO3 [i.e., (La0.25Sr0.75)TiO3], we reveal the strong electron-lattice-orbital coupling, which is manifested by extremely increased tetragonality and the corresponding metal-to-insulator transition. Our findings open the way of an active tuning of the charge-lattice-orbital coupling to obtain new functionalities relevant to emerging nanoelectronic devices.
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Affiliation(s)
- Kitae Eom
- School of Advanced Materials Science and Engineering, Sungkyunkwan University , Suwon 16419, Republic of Korea
| | - Euiyoung Choi
- School of Advanced Materials Science and Engineering, Sungkyunkwan University , Suwon 16419, Republic of Korea
| | - Jonghyun Yoon
- School of Advanced Materials Science and Engineering, Sungkyunkwan University , Suwon 16419, Republic of Korea
| | - Minsu Choi
- School of Advanced Materials Science and Engineering, Sungkyunkwan University , Suwon 16419, Republic of Korea
| | - Kyung Song
- Department of Materials Modeling and Characterization, Korea Institute of Materials Science , Changwon 51508, Republic of Korea
| | - Si-Young Choi
- Department of Materials Modeling and Characterization, Korea Institute of Materials Science , Changwon 51508, Republic of Korea
| | - Daesu Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53792, United States
| | - Jung-Woo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53792, United States
| | - Chang-Beom Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53792, United States
| | - Jaichan Lee
- School of Advanced Materials Science and Engineering, Sungkyunkwan University , Suwon 16419, Republic of Korea
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27
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Tsai MS, Li CS, Guo ST, Song MY, Singh AK, Lee WL, Chu MW. Off-Stoichiometry Driven Carrier Density Variation at the Interface of LaAlO 3/SrTiO 3. Sci Rep 2017; 7:1770. [PMID: 28496105 PMCID: PMC5431992 DOI: 10.1038/s41598-017-02039-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 04/05/2017] [Indexed: 11/28/2022] Open
Abstract
The interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted enormous interests due to its rich physical phenomena, such as metallic nature, magnetism and superconductivity. In this work, we report our experimental investigations on the influence of the LAO stoichiometry to the metallic interface. Taking advantage of the oxide molecular beam epitaxy (MBE) technique, a series of high quality LAO films with different nominal La/Al ratios and LAO thicknesses were grown on the TiO2-terminated STO substrates, where systematic variations of the LAO lattice constant and transport property were observed. In particular, the sheet density can be largely reduced by nearly an order of magnitude with merely about 20% increase in the nominal La/Al ratio. Our finding provides an effective method on tuning the electron density of the two-dimensional electron liquid (2DEL) at the LAO/STO interface.
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Affiliation(s)
- Ming-Shiu Tsai
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan
| | - Chi-Sheng Li
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan
| | - Shih-Ting Guo
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan
| | - Ming-Yuan Song
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan
| | - Akhilesh Kr Singh
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan.
| | - Wei-Li Lee
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan.
| | - M-W Chu
- Center for Condensed Matter Sciences, National Taiwan University, Taipei, 10617, Taiwan
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28
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Wang F, Ren Z, Tian H, Yang SA, Xie Y, Lu Y, Jiang J, Han G, Yang K. Interfacial Multiferroics of TiO 2/PbTiO 3 Heterostructure Driven by Ferroelectric Polarization Discontinuity. ACS APPLIED MATERIALS & INTERFACES 2017; 9:1899-1906. [PMID: 27990804 DOI: 10.1021/acsami.6b13183] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Novel phenomena appear when two different oxide materials are combined together to form an interface. For example, at the interface of LaAlO3/SrTiO3, two-dimensional conductive states form to avoid the polar discontinuity, and magnetic properties are found at such an interface. In this work, we propose a new type of interface between two nonmagnetic and nonpolar oxides that could host a magnetic state, where it is the ferroelectric polarization discontinuity instead of the polar discontinuity that leads to the charge transfer, forming the interfacial magnetic state. As a concrete example, we investigate by first-principles calculations the heterostructures made of ferroelectric perovskite oxide PbTiO3 and nonferroelectric polarized oxide TiO2. We show that charge is transferred to the interfacial layer forming an interfacial ferromagnetic ordering that may persist up to room temperature. Especially, the strong coupling between bulk ferroelectric polarization and interface ferromagnetism represents a new type of magnetoelectric effect, which provides an ideal platform for exploring the intriguing interfacial multiferroics. The findings here are important not only for fundamental science but also for promising applications in nanoscale electronics and spintronics.
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Affiliation(s)
| | | | | | - Shengyuan A Yang
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design , Singapore 487372, Singapore
| | | | | | | | | | - Kesong Yang
- Department of NanoEngineering, University of California , San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
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29
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Jin MJ, Moon SY, Park J, Modepalli V, Jo J, Kim SI, Koo HC, Min BC, Lee HW, Baek SH, Yoo JW. Nonlocal Spin Diffusion Driven by Giant Spin Hall Effect at Oxide Heterointerfaces. NANO LETTERS 2017; 17:36-43. [PMID: 27935722 DOI: 10.1021/acs.nanolett.6b03050] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A two-dimensional electron gas emerged at a LaAlO3/SrTiO3 interface is an ideal system for "spin-orbitronics" as the structure itself strongly couple the spin and orbital degree of freedom through the Rashba spin-orbit interaction. One of core experiments toward this direction is the nonlocal spin transport measurement, which has remained elusive due to the low spin injection efficiency to this system. Here we bypass the problem by generating a spin current not through the spin injection from outside but instead through the inherent spin Hall effect and demonstrate the nonlocal spin transport. The analysis on the nonlocal spin voltage, confirmed by the signature of a Larmor spin precession and its length dependence, displays that both D'yakonov-Perel' and Elliott-Yafet mechanisms involve in the spin relaxation at low temperature. Our results show that the oxide heterointerface is highly efficient in spin-charge conversion with exceptionally strong spin Hall coefficient γ ∼ 0.15 ± 0.05 and could be an outstanding platform for the study of coupled charge and spin transport phenomena and their electronic applications.
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Affiliation(s)
- Mi-Jin Jin
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan, 44919, Korea
| | - Seon Young Moon
- Center for Electronic Materials, Korea Institute of Science and Technology , Seoul 02792, Korea
| | - Jungmin Park
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan, 44919, Korea
| | - Vijayakumar Modepalli
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan, 44919, Korea
| | - Junhyeon Jo
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan, 44919, Korea
| | - Shin-Ik Kim
- Center for Electronic Materials, Korea Institute of Science and Technology , Seoul 02792, Korea
- Department of Nanomaterials Science and Technology, Korea University of Science and Technology , Daejeon, 34113, Korea
| | - Hyun Cheol Koo
- Center for Spintronics, Korea Institute of Science and Technology , Seoul 02792, Korea
- KU-KIST Graduate School of Converging Science and Technology, Korea University , Seoul, 02481, Korea
| | - Byoung-Chul Min
- Department of Nanomaterials Science and Technology, Korea University of Science and Technology , Daejeon, 34113, Korea
- Center for Spintronics, Korea Institute of Science and Technology , Seoul 02792, Korea
| | - Hyun-Woo Lee
- PCTP and Department of Physics, Pohang University of Science and Technology , Pohang 37673, Korea
| | - Seung-Hyub Baek
- Center for Electronic Materials, Korea Institute of Science and Technology , Seoul 02792, Korea
- Department of Nanomaterials Science and Technology, Korea University of Science and Technology , Daejeon, 34113, Korea
| | - Jung-Woo Yoo
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan, 44919, Korea
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30
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Gunkel F, Hoffmann-Eifert S, Heinen RA, Christensen DV, Chen YZ, Pryds N, Waser R, Dittmann R. Thermodynamic Ground States of Complex Oxide Heterointerfaces. ACS APPLIED MATERIALS & INTERFACES 2017; 9:1086-1092. [PMID: 27992161 DOI: 10.1021/acsami.6b12706] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The formation mechanism of 2-dimensional electron gases (2DEGs) at heterointerfaces between nominally insulating oxides is addressed with a thermodynamical approach. We provide a comprehensive analysis of the thermodynamic ground states of various 2DEG systems directly probed in high temperature equilibrium conductivity measurements. We unambiguously identify two distinct classes of oxide heterostructures: For epitaxial perovskite/perovskite heterointerfaces (LaAlO3/SrTiO3, NdGaO3/SrTiO3, and (La,Sr)(Al,Ta)O3/SrTiO3), we find the 2DEG formation being based on charge transfer into the interface, stabilized by the electric field in the space charge region. In contrast, for amorphous LaAlO3/SrTiO3 and epitaxial γ-Al2O3/SrTiO3 heterostructures, the 2DEG formation mainly relies on the formation and accumulation of oxygen vacancies. This class of 2DEG structures exhibits an unstable interface reconstruction associated with a quenched nonequilibrium state.
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Affiliation(s)
- F Gunkel
- Institute of Electronic Materials, IWE2, RWTH Aachen University , 52056 Aachen, Germany
| | - S Hoffmann-Eifert
- Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany
| | - R A Heinen
- Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany
| | - D V Christensen
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - Y Z Chen
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - N Pryds
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
| | - R Waser
- Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany
| | - R Dittmann
- Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany
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31
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Cheng J, Nazir S, Yang K. First-Principles Prediction of Two-Dimensional Electron Gas Driven by Polarization Discontinuity in Nonpolar/Nonpolar AHfO 3/SrTiO 3 (A = Ca, Sr, and Ba) Heterostructures. ACS APPLIED MATERIALS & INTERFACES 2016; 8:31959-31967. [PMID: 27800684 DOI: 10.1021/acsami.6b06907] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
By using first-principles electronic structure calculations, we explored the possibility of producing two-dimensional electron gas (2DEG) in nonpolar/nonpolar AHfO3/SrTiO3 (A = Ca, Sr, and Ba) heterostructures. Two types of nonpolar/nonpolar interfaces, (AO)0/(TiO2)0 and (HfO2)0/(SrO)0, each with AO and HfO2 surface terminations, are modeled, respectively. The polarization domain and resulting interfacial electronic property are found to be more sensitive to the surface termination of the film rather than the interface model. As film thickness increases, an insulator-to-metal transition is found in all the heterostructures with HfO2 surface termination: for (AO)0/(TiO2)0 interfaces, predicted critical film thickness for an insulator-to-metal transition is about 7, 6, and 3 unit cells for CaHfO3/SrTiO3, SrHfO3/SrTiO3, and BaHfO3/SrTiO3, respectively; for (HfO2)0/(SrO)0 interfaces, the critical film thickness is about 7.5, 5.5, and 4.5 unit cells, respectively. In contrast, for the heterostructures with AO surface termination, CaHfO3/SrTiO3 exhibits a much larger critical film thickness about 11-12 unit cells for an insulator-to-metal transition; while SrHfO3/SrTiO3 and BaHfO3/SrTiO3 do not show any polarization behavior even film thickness increases up to 20 unit cells. The strain-induced polarization behavior was well-elucidated from energy versus polarization profile. This work is expected to stimulate further experimental investigation to the interfacial conductivity in the nonpolar/nonpolar AHfO3/SrTiO3 HS.
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Affiliation(s)
- Jianli Cheng
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Safdar Nazir
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Kesong Yang
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
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32
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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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33
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Hong S, Nakhmanson SM, Fong DD. Screening mechanisms at polar oxide heterointerfaces. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2016; 79:076501. [PMID: 27308889 DOI: 10.1088/0034-4885/79/7/076501] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The interfaces of polar oxide heterostructures can display electronic properties unique from the oxides they border, as they require screening from either internal or external sources of charge. The screening mechanism depends on a variety of factors, including the band structure at the interface, the presence of point defects or adsorbates, whether or not the oxide is ferroelectric, and whether or not an external field is applied. In this review, we discuss both theoretical and experimental aspects of different screening mechanisms, giving special emphasis to ways in which the mechanism can be altered to provide novel or tunable functionalities. We begin with a theoretical introduction to the problem and highlight recent progress in understanding the impact of point defects on polar interfaces. Different case studies are then discussed, for both the high thickness regime, where interfaces must be screened and each interface can be considered separately, and the low thickness regime, where the degree and nature of screening can be manipulated and the interfaces are close enough to interact. We end with a brief outlook toward new developments in this rapidly progressing field.
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Affiliation(s)
- Seungbum Hong
- Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA. Department of Materials Science & Engineering, KAIST, Daejeon 305-701, Korea
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34
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Wang Y, Tang W, Cheng J, Behtash M, Yang K. Creating Two-Dimensional Electron Gas in Polar/Polar Perovskite Oxide Heterostructures: First-Principles Characterization of LaAlO3/A(+)B(5+)O3. ACS APPLIED MATERIALS & INTERFACES 2016; 8:13659-13668. [PMID: 27160513 DOI: 10.1021/acsami.6b02399] [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
By using first-principles electronic structure calculations, we explored the possibility of producing two-dimensional electron gas (2DEG) at the polar/polar (LaO)(+)/(BO2)(+) interface in the LaAlO3/A(+)B(5+)O3 (A = Na and K, B = Nb and Ta) heterostructures (HS). Unlike the prototype polar/nonpolar LaAlO3/SrTiO3 HS system where there exists a least film thickness of four LaAlO3 unit cells to have an insulator-to-metal transition, we found that the polar/polar LaAlO3/A(+)B(5+)O3 HS systems are intrinsically conducting at their interfaces without an insulator-to-metal transition. The interfacial charge carrier densities of these polar/polar HS systems are on the order of 10(14) cm(-2), much larger than that of the LaAlO3/SrTiO3 system. This is mainly attributed to two donor layers, i.e., (LaO)(+) and (BO2)(+) (B = Nb and Ta), in the polar/polar LaAlO3/A(+)B(5+)O3 systems, while only one (LaO)(+) donor layer in the polar/nonpolar LaAlO3/SrTiO3 system. In addition, it is expected that, due to less localized Nb 4d and Ta 5d orbitals with respect to Ti 3d orbitals, these LaAlO3/A(+)B(5+)O3 HS systems can exhibit potentially higher electron mobility because of their smaller electron effective mass than that in the LaAlO3/SrTiO3 system. Our results demonstrate that the electronic reconstruction at the polar/polar interface could be an alternative way to produce superior 2DEG in the perovskite-oxide-based HS systems.
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Affiliation(s)
- Yaqin Wang
- State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China , Chengdu, Sichuan 610054, P. R. China
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Wu Tang
- State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China , Chengdu, Sichuan 610054, P. R. China
| | - Jianli Cheng
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Maziar Behtash
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Kesong Yang
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
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Zhuang HL, Zhang L, Xu H, Kent PRC, Ganesh P, Cooper VR. Tunable one-dimensional electron gas carrier densities at nanostructured oxide interfaces. Sci Rep 2016; 6:25452. [PMID: 27151049 PMCID: PMC4858694 DOI: 10.1038/srep25452] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 04/15/2016] [Indexed: 11/29/2022] Open
Abstract
The emergence of two-dimensional metallic states at the LaAlO3/SrTiO3 (LAO/STO) heterostructure interface is known to occur at a critical thickness of four LAO layers. This insulator to-metal transition can be explained through the “polar catastrophe” mechanism arising from the divergence of the electrostatic potential at the LAO surface. Here, we demonstrate that nanostructuring can be effective in reducing or eliminating this critical thickness. Employing a modified “polar catastrophe” model, we demonstrate that the nanowire heterostructure electrostatic potential diverges more rapidly as a function of layer thickness than in a regular heterostructure. Our first-principles calculations indicate that for nanowire heterostructures a robust one-dimensional electron gas (1DEG) can be induced, consistent with recent experimental observations of 1D conductivity at LAO/STO steps. Similar to LAO/STO 2DEGs, we predict that the 1D charge density decays laterally within a few unit cells away from the nanowire; thus providing a mechanism for tuning the carrier dimensionality between 1D and 2D conductivity. Our work provides insight into the creation and manipulation of charge density at an oxide heterostructure interface and therefore may be beneficial for future nanoelectronic devices and for the engineering of novel quantum phases.
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Affiliation(s)
- Houlong L Zhuang
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
| | - Lipeng Zhang
- Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Haixuan Xu
- Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996, United States
| | - P R C Kent
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, Tennessee 37831, United States.,Computer Science and Mathematics Division, Oak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
| | - P Ganesh
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
| | - Valentino R Cooper
- Materials Science and Technology Division, Oak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
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Nazir S, Cheng J, Yang K. Creating Two-Dimensional Electron Gas in Nonpolar/Nonpolar Oxide Interface via Polarization Discontinuity: First-Principles Analysis of CaZrO3/SrTiO3 Heterostructure. ACS APPLIED MATERIALS & INTERFACES 2016; 8:390-399. [PMID: 26649746 DOI: 10.1021/acsami.5b09107] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We studied strain-induced polarization and resulting conductivity in the nonpolar/nonpolar CaZrO3/SrTiO3 (CZO/STO) heterostructure (HS) system by means of first-principles electronic structure calculations. By modeling four types of CZO/STO HS-based slab systems, i.e., TiO2/CaO and SrO/ZrO2 interface models with CaO and ZrO2 surface terminations in each model separately, we found that the lattice-mismatch-induced compressive strain leads to a strong polarization in the CZO film and that as the CZO film thickness increases there exists an insulator-to-metal transition. The polarization direction and critical thickness of the CZO film for forming interfacial metallic states depend on the surface termination of CZO film in both types of interface models. In the TiO2/CaO and SrO/ZrO2 interface models with CaO surface termination, the strong polarization drives the charge transfer from the CZO film to the first few TiO2 layers in the STO substrate, leading to the formation of two-dimensional electron gas (2DEG) at the interface. In the HS models with ZrO2 surface termination, two polarization domains with opposite directions are in the CZO film, which results in the charge transfer from the middle CZO layer to the interface and surface, respectively, leading to the coexistence of the 2DEG on the interface and the two-dimensional hole gas (2DHG) at the middle CZO layer. These findings open a new avenue to achieve 2DEG (2DHG) in perovskite-based HS systems via polarization discontinuity.
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Affiliation(s)
- Safdar Nazir
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Jianli Cheng
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Kesong Yang
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
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