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Santana JA, Krogel JT, Okamoto S, Reboredo FA. Electron Confinement and Magnetism of (LaTiO3)1/(SrTiO3)5 Heterostructure: A Diffusion Quantum Monte Carlo Study. J Chem Theory Comput 2019; 16:643-650. [DOI: 10.1021/acs.jctc.9b00678] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Juan A. Santana
- Department of Chemistry, University of Puerto Rico at Cayey, P.O. Box 372230, Cayey, PR 00737-2230, United States
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Jaron T. Krogel
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Satoshi Okamoto
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Fernando A. Reboredo
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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2
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Mori R, Marshall PB, Ahadi K, Denlinger JD, Stemmer S, Lanzara A. Controlling a Van Hove singularity and Fermi surface topology at a complex oxide heterostructure interface. Nat Commun 2019; 10:5534. [PMID: 31797932 PMCID: PMC6892806 DOI: 10.1038/s41467-019-13046-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 10/16/2019] [Indexed: 11/10/2022] Open
Abstract
The emergence of saddle-point Van Hove singularities (VHSs) in the density of states, accompanied by a change in Fermi surface topology, Lifshitz transition, constitutes an ideal ground for the emergence of different electronic phenomena, such as superconductivity, pseudo-gap, magnetism, and density waves. However, in most materials the Fermi level, \documentclass[12pt]{minimal}
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\begin{document}$${E}_{{\rm{F}}}$$\end{document}EF, is too far from the VHS where the change of electronic topology takes place, making it difficult to reach with standard chemical doping or gating techniques. Here, we demonstrate that this scenario can be realized at the interface between a Mott insulator and a band insulator as a result of quantum confinement and correlation enhancement, and easily tuned by fine control of layer thickness and orbital occupancy. These results provide a tunable pathway for Fermi surface topology and VHS engineering of electronic phases. A singularity in a material’s density of states at the Fermi energy can drive the formation of unconventional electronic phases. Here the authors show a Van Hove singularity is tunable across the Fermi energy in an oxide heterostructure, leading to enhanced electronic correlations.
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Affiliation(s)
- Ryo Mori
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.,Applied Science & Technology, University of California, Berkeley, CA, 94720, USA
| | - Patrick B Marshall
- Materials Department, University of California, Santa Barbara, CA, 93106-5050, USA
| | - Kaveh Ahadi
- Materials Department, University of California, Santa Barbara, CA, 93106-5050, USA
| | - Jonathan D Denlinger
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Susanne Stemmer
- Materials Department, University of California, Santa Barbara, CA, 93106-5050, USA
| | - Alessandra Lanzara
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. .,Department of Physics, University of California, Berkeley, CA, 94720, USA.
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Bhandari C, Satpathy S. Two dimensional electron gas in the [Formula: see text]-doped iridates with strong spin-orbit coupling: La[Formula: see text]Sr 2IrO 4. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:435505. [PMID: 31272089 DOI: 10.1088/1361-648x/ab2f3f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Iridates are of considerable current interest because of the strong spin-orbit coupling that leads to a variety of new phenomena. Using density-functional studies, we predict the formation of a spin-orbital entangled two dimensional electron gas (2DEG) in the [Formula: see text]-doped iridate La[Formula: see text]Sr2IrO4, where a single SrO layer is replaced by a LaO layer. The extra La electron resides close to the [Formula: see text]-doped layer, partially occupying the [Formula: see text] upper Hubbard band and thereby making the interface metallic. The magnetic structure of the bulk is destroyed near the interface, with the Ir0 layer closest to the interface becoming non-magnetic, while the next layer (Ir1) continues to maintain the AFM structure of the bulk, but with a reduced magnetic moment. The Fermi surface consists of a hole pocket and an electron pocket, located in two different Ir layers (Ir0 and Ir1), with both carriers derived from the [Formula: see text] upper Hubbard band. The presence of both electrons and holes at the [Formula: see text]-doped interface suggests unusual transport properties, leading to possible device applications.
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Affiliation(s)
- Churna Bhandari
- Department of Physics & Astronomy, University of Columbia Missouri, Columbia, MO 65211, United States of America
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4
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Ghising P, Das D, Das S, Hossain Z. Kondo effect with tunable spin-orbit interaction in LaTiO 3/CeTiO 3/SrTiO 3 heterostructure. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:285002. [PMID: 29855435 DOI: 10.1088/1361-648x/aac977] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We have fabricated epitaxial films of CeTiO3 (CTO) on (0 0 1) oriented SrTiO3 (STO) substrates, which exhibit highly insulating and diamagnetic properties. X-ray photoelectron spectroscopy was used to establish the 3+ valence state of the Ce and Ti ions. Furthermore, we have also fabricated δ (CTO) doped LaTiO3 (LTO)/SrTiO3 thin films which exhibit variety of interesting properties including Kondo effect and spin-orbit interaction (SOI) at low temperatures. The SOI shows a non-monotonic behaviour as the thickness of the CTO layer is increased and is reflected in the value of characteristic SOI field ([Formula: see text]) obtained from weak anti-localization fitting. The maximum value of [Formula: see text] is 1.00 T for δ layer thickness of 6 u.c. This non-monotonic behaviour of SOI is attributed to the strong screening of the confining potential at the interface. The screening effect is enhanced by the CTO layer thickness and the dielectric constant of STO which increases at low temperatures. Due to the strong screening, electrons confined at the interface are spread deeper into the STO bulk where it starts to populate the Ti [Formula: see text] subbands; consequently the Fermi level crosses over from [Formula: see text] to the [Formula: see text] subbands. At the crossover region of [Formula: see text] where there is orbital mixing, SOI goes through a maximum.
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Affiliation(s)
- Pramod Ghising
- Department of Physics, Condensed Matter-Low Dimensional Systems Laboratory, Indian Institute of Technology, Kanpur-208016, India
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5
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Veit MJ, Arras R, Ramshaw BJ, Pentcheva R, Suzuki Y. Nonzero Berry phase in quantum oscillations from giant Rashba-type spin splitting in LaTiO 3/SrTiO 3 heterostructures. Nat Commun 2018; 9:1458. [PMID: 29654231 PMCID: PMC5899139 DOI: 10.1038/s41467-018-04014-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Accepted: 03/26/2018] [Indexed: 11/17/2022] Open
Abstract
The manipulation of the spin degrees of freedom in a solid has been of fundamental and technological interest recently for developing high-speed, low-power computational devices. There has been much work focused on developing highly spin-polarized materials and understanding their behavior when incorporated into so-called spintronic devices. These devices usually require spin splitting with magnetic fields. However, there is another promising strategy to achieve spin splitting using spatial symmetry breaking without the use of a magnetic field, known as Rashba-type splitting. Here we report evidence for a giant Rashba-type splitting at the interface of LaTiO3 and SrTiO3. Analysis of the magnetotransport reveals anisotropic magnetoresistance, weak anti-localization and quantum oscillation behavior consistent with a large Rashba-type splitting. It is surprising to find a large Rashba-type splitting in 3d transition metal oxide-based systems such as the LaTiO3/SrTiO3 interface, but it is promising for the development of a new kind of oxide-based spintronics. Rashba-type splitting is an effective way to manipulate the spin degrees of freedom in a solid without external magnetic field. Here, the authors demonstrate a strong Rashba-type splitting at the interface of LaTiO3 and SrTiO3 which is promising for the development of oxide-based spintronics.
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Affiliation(s)
- M J Veit
- Department of Applied Physics and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, 94305, USA.
| | - R Arras
- CEMES, University of Toulouse, CNRS, UPS, 29, rue Jeanne Marvig, 31055, Toulouse, France
| | - B J Ramshaw
- Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.,Laboratory for Atomic and Solid State Physics, Cornell University, Ithaca, NY, 14853, USA
| | - R Pentcheva
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, Lotharstrasse 1, 47057, Duisburg, Germany
| | - Y Suzuki
- Department of Applied Physics and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, 94305, USA
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6
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Cao Y, Yang Z, Kareev M, Liu X, Meyers D, Middey S, Choudhury D, Shafer P, Guo J, Freeland JW, Arenholz E, Gu L, Chakhalian J. Magnetic Interactions at the Nanoscale in Trilayer Titanates. PHYSICAL REVIEW LETTERS 2016; 116:076802. [PMID: 26943550 DOI: 10.1103/physrevlett.116.076802] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Indexed: 06/05/2023]
Abstract
We report on the phase diagram of competing magnetic interactions at the nanoscale in engineered ultrathin trilayer heterostructures of LaTiO_{3}/SrTiO_{3}/YTiO_{3}, in which the interfacial inversion symmetry is explicitly broken. Combined atomic layer resolved scanning transmission electron microscopy with electron energy loss spectroscopy and electrical transport have confirmed the formation of a spatially separated two-dimensional electron liquid and high density two-dimensional localized magnetic moments at the LaTiO_{3}/SrTiO_{3} and SrTiO_{3}/YTiO_{3} interfaces, respectively. Resonant soft x-ray linear dichroism spectroscopy has demonstrated the presence of orbital polarization of the conductive LaTiO_{3}/SrTiO_{3} and localized SrTiO_{3}/YTiO_{3} electrons. Our results provide a route with prospects for exploring new magnetic interfaces, designing a tunable two-dimensional d-electron Kondo lattice, and potential spin Hall applications.
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Affiliation(s)
- Yanwei Cao
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - Zhenzhong Yang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
| | - M Kareev
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - Xiaoran Liu
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - D Meyers
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - S Middey
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - D Choudhury
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
- Department of Physics, Indian Institute of Technology, Kharagpur 721302, India
| | - P Shafer
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Jiandong Guo
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
- Collaborative Innovation Center of Quantum Matter, Beijing 100190, People's Republic of China
| | - J W Freeland
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - E Arenholz
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Lin Gu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
- Collaborative Innovation Center of Quantum Matter, Beijing 100190, People's Republic of China
| | - J Chakhalian
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
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7
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Wu L, Bo M, Guo Y, Wang Y, Li C, Huang Y, Sun CQ. Skin Bond Electron Relaxation Dynamics of Germanium Manipulated by Interactions with H2 , O2 , H2 O, H2 O2 , HF, and Au. Chemphyschem 2016; 17:310-6. [PMID: 26488077 DOI: 10.1002/cphc.201500769] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Indexed: 11/10/2022]
Abstract
Although germanium performs amazingly well at sites surrounding hetero-coordinated impurities and under-coordinated defects or skins with unusual properties, having important impact on electronic and optical devices, understanding the behavior of the local bonds and electrons at such sites remains a great challenge. Here we show that a combination of density functional theory calculations, zone-resolved X-ray photoelectron spectroscopy, and bond order length strength correlation mechanism has enabled us to clarify the physical origin of the Ge 3d core-level shift for the under-coordinated (111) and (100) skin with and without hetero-coordinated H2 , O2 , H2 O, H2 O2 , HF impurities. The Ge 3d level shifts from 27.579 (for an isolated atom) by 1.381 to 28.960 eV upon bulk formation. Atomic under-coordination shifts the binding energy further to 29.823 eV for the (001) and to 29.713 eV for the (111) monolayer skin. Addition of O2 , HF, H2 O, H2 O2 and Au impurities results in quantum entrapment by different amounts, but H adsorption leads to polarization.
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Affiliation(s)
- Lihong Wu
- Key Laboratory of Low-dimensional Materials and Application Technology (Ministry of Education), School of Materials Science and Engineering, Xiangtan University, Xiangtan, 411105, China
| | - Maolin Bo
- Key Laboratory of Low-dimensional Materials and Application Technology (Ministry of Education), School of Materials Science and Engineering, Xiangtan University, Xiangtan, 411105, China
| | - Yongling Guo
- Key Laboratory of Low-dimensional Materials and Application Technology (Ministry of Education), School of Materials Science and Engineering, Xiangtan University, Xiangtan, 411105, China
| | - Yan Wang
- School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan, 411201, China
| | - Can Li
- Institute for Coordination Bond Metrology and Engineering, College of Materials Science and Engineering, China Jiliang University, Hangzhou, 310018, China
| | - Yongli Huang
- Key Laboratory of Low-dimensional Materials and Application Technology (Ministry of Education), School of Materials Science and Engineering, Xiangtan University, Xiangtan, 411105, China.
| | - Chang Q Sun
- NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore.
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8
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Labram JG, Lin YH, Anthopoulos TD. Exploring Two-Dimensional Transport Phenomena in Metal Oxide Heterointerfaces for Next-Generation, High-Performance, Thin-Film Transistor Technologies. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2015; 11:5472-5482. [PMID: 26349850 DOI: 10.1002/smll.201501350] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Revised: 06/16/2015] [Indexed: 06/05/2023]
Abstract
In the last decade, metal oxides have emerged as a fascinating class of electronic material, exhibiting a wide range of unique and technologically relevant characteristics. For example, thin-film transistors formed from amorphous or polycrystalline metal oxide semiconductors offer the promise of low-cost, large-area, and flexible electronics, exhibiting performances comparable to or in excess of incumbent silicon-based technologies. Atomically flat interfaces between otherwise insulating or semiconducting complex oxides, are also found to be highly conducting, displaying 2-dimensional (2D) charge transport properties, strong correlations, and even superconductivity. Field-effect devices employing such carefully engineered interfaces are hoped to one day compete with traditional group IV or III-V semiconductors for use in the next-generation of high-performance electronics. In this Concept article we provide an overview of the different metal oxide transistor technologies and potential future research directions. In particular, we look at the recent reports of multilayer oxide thin-film transistors and the possibility of 2D electron transport in these disordered/polycrystalline systems and discuss the potential of the technology for applications in large-area electronics.
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Affiliation(s)
- John G Labram
- Department of Physics and Centre for Plastic Electronics, Blackett Laboratory, Imperial College London, London, SW7 2BW, UK
| | - Yen-Hung Lin
- Department of Physics and Centre for Plastic Electronics, Blackett Laboratory, Imperial College London, London, SW7 2BW, UK
| | - Thomas D Anthopoulos
- Department of Physics and Centre for Plastic Electronics, Blackett Laboratory, Imperial College London, London, SW7 2BW, UK
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9
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Liu X, Zhang X, Bo M, Li L, Tian H, Nie Y, Sun Y, Xu S, Wang Y, Zheng W, Sun CQ. Coordination-resolved electron spectrometrics. Chem Rev 2015; 115:6746-810. [PMID: 26110615 DOI: 10.1021/cr500651m] [Citation(s) in RCA: 111] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Xinjuan Liu
- †Institute of Coordination Bond Metrology and Engineering, College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, China
| | - Xi Zhang
- ‡Institute of Nanosurface Science and Engineering, Shenzhen University, Shenzhen 518060, China
| | - Maolin Bo
- §Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education) and School of Materials Science and Engineering, Xiangtan University, Hunan 411105, China
| | - Lei Li
- ∥School of Materials Science, Jilin University, Changchun 130012, China
| | - Hongwei Tian
- ∥School of Materials Science, Jilin University, Changchun 130012, China
| | - Yanguang Nie
- ⊥School of Science, Jiangnan University, Wuxi 214122, China
| | - Yi Sun
- #Harris School of Public Policy, University of Chicago, Chicago, Illinois 60637, United States
| | - Shiqing Xu
- †Institute of Coordination Bond Metrology and Engineering, College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, China
| | - Yan Wang
- ∇School of Information Technology, Hunan University of Science and Technology, Xiangtan 411201, China
| | - Weitao Zheng
- ∥School of Materials Science, Jilin University, Changchun 130012, China
| | - Chang Q Sun
- ○NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
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10
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Moon EJ, Colby R, Wang Q, Karapetrova E, Schlepütz CM, Fitzsimmons MR, May SJ. Spatial control of functional properties via octahedral modulations in complex oxide superlattices. Nat Commun 2014; 5:5710. [DOI: 10.1038/ncomms6710] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Accepted: 10/29/2014] [Indexed: 11/09/2022] Open
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11
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Xiang X, Qiao L, Xiao HY, Gao F, Zu XT, Li S, Zhou WL. Effects of surface defects on two-dimensional electron gas at NdAlO3/SrTiO3 interface. Sci Rep 2014; 4:5477. [PMID: 24969627 PMCID: PMC4073165 DOI: 10.1038/srep05477] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Accepted: 06/06/2014] [Indexed: 11/23/2022] Open
Abstract
Density functional theory calculations of NdAlO3/SrTiO3 heterostructure show that two-dimensional electron gas (2-DEG) is produced at the interface with a built-in potential of ~0.3 eV per unit cell. The effects of surface defects on the phase stability and electric field of 2-DEG have been investigated. It is found that oxygen vacancy is easily to form on the NdAlO3(001) surface, with a low threshold displacement energy and a low formation energy. This point defect results in surface reconstruction and the formation of a zigzag -Al-O-Al- chain, which quenches the built-in potential and enhances the carrier density significantly. These results will provide fundamental insights into understanding how surface defects influence the electronic behavior of 2-DEG and tuning their electronic properties through surface modification.
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Affiliation(s)
- X Xiang
- School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
| | - L Qiao
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - H Y Xiao
- School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
| | - F Gao
- Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA
| | - X T Zu
- School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
| | - S Li
- School of Material Science and Engineering, University of New South Wales, Sydney, 2052, Australia
| | - W L Zhou
- Advanced Materials Research Institute, University of New Orleans, New Orleans, LA, 70148, USA
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12
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Biscaras J, Bergeal N, Hurand S, Grossetête C, Rastogi A, Budhani RC, LeBoeuf D, Proust C, Lesueur J. Two-dimensional superconducting phase in LaTiO3/SrTiO3 heterostructures induced by high-mobility carrier doping. PHYSICAL REVIEW LETTERS 2012; 108:247004. [PMID: 23004312 DOI: 10.1103/physrevlett.108.247004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Indexed: 06/01/2023]
Abstract
In this Letter, we show that a superconducting two-dimensional electron gas is formed at the LaTiO3/SrTiO3 interface whose transition temperature can be modulated by a back-gate voltage. The gas consists of two types of carriers: a majority of low-mobility carriers always present, and a few high-mobility ones that can be injected by electrostatic doping. The calculation of the electron spatial distribution in the confinement potential shows that the high-mobility electrons responsible for superconductivity set at the edge of the gas whose extension can be tuned by the field effect.
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Affiliation(s)
- J Biscaras
- LPEM-UMR8213/CNRS-ESPCI ParisTech-UPMC, 10 rue Vauquelin-75005 Paris, France
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13
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Rissner F, Egger DA, Natan A, Körzdörfer T, Kümmel S, Kronik L, Zojer E. Collectively induced quantum-confined Stark effect in monolayers of molecules consisting of polar repeating units. J Am Chem Soc 2011; 133:18634-45. [PMID: 21955058 PMCID: PMC3217729 DOI: 10.1021/ja203579c] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Indexed: 11/27/2022]
Abstract
The electronic structure of terpyrimidinethiols is investigated by means of density-functional theory calculations for isolated molecules and monolayers. In the transition from molecule to self-assembled monolayer (SAM), we observe that the band gap is substantially reduced, frontier states increasingly localize on opposite sides of the SAM, and this polarization in several instances is in the direction opposite to the polarization of the overall charge density. This behavior can be analyzed by analogy to inorganic semiconductor quantum-wells, which, as the SAMs studied here, can be regarded as semiperiodic systems. There, similar observations are made under the influence of a, typically external, electric field and are known as the quantum-confined Stark effect. Without any external perturbation, in oligopyrimidine SAMs one encounters an energy gradient that is generated by the dipole moments of the pyrimidine repeat units. It is particularly strong, reaching values of about 1.6 eV/nm, which corresponds to a substantial electric field of 1.6 × 10(7) V/cm. Close-lying σ- and π-states turn out to be a particular complication for a reliable description of the present systems, as their order is influenced not only by the docking groups and bonding to the metal, but also by the chosen computational approach. In the latter context we demonstrate that deliberately picking a hybrid functional allows avoiding pitfalls due to the infamous self-interaction error. Our results show that when aiming to build a monolayer with a specific electronic structure one can not only resort to the traditional technique of modifying the molecular structure of the constituents, but also try to exploit collective electronic effects.
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Affiliation(s)
- Ferdinand Rissner
- Institute of Solid State Physics, Graz University of Technology, 8010 Graz, Austria
| | - David A. Egger
- Institute of Solid State Physics, Graz University of Technology, 8010 Graz, Austria
| | - Amir Natan
- Department of Materials and Interfaces, Weizmann Institute of Science, 76100 Rehovoth, Israel
| | - Thomas Körzdörfer
- Theoretical Physics IV, University of Bayreuth, 95440 Bayreuth, Germany
| | - Stephan Kümmel
- Theoretical Physics IV, University of Bayreuth, 95440 Bayreuth, Germany
| | - Leeor Kronik
- Department of Materials and Interfaces, Weizmann Institute of Science, 76100 Rehovoth, Israel
| | - Egbert Zojer
- Institute of Solid State Physics, Graz University of Technology, 8010 Graz, Austria
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14
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Putzel GG, Uline MJ, Szleifer I, Schick M. Interleaflet coupling and domain registry in phase-separated lipid bilayers. Biophys J 2011; 100:996-1004. [PMID: 21320444 DOI: 10.1016/j.bpj.2011.01.021] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2010] [Revised: 01/08/2011] [Accepted: 01/11/2011] [Indexed: 12/23/2022] Open
Abstract
There is clear evidence of an interleaflet coupling in model lipid/cholesterol membranes exhibiting liquid-liquid phase separation. The strength of this coupling is quantified by the mismatch free energy, γ. We calculate it using a molecular mean-field model of a phase-separated lipid/cholesterol bilayer and obtain values that increase as the concentration of saturated lipids in the coexisting phases is increased. These values lie in the range 0.01-0.03 k(B)T/nm(2). We clarify the relationship between the interleaflet coupling and the extent of interleaflet alignment of liquid domains by analyzing a statistical mechanical model of coupled fluctuating domain interfaces. The model is solved exactly using the correspondence between statistical mechanics and quantum mechanics, yielding an expression for the characteristic size of fluctuations out of domain registry. This length scale depends only weakly on the strength of the interleaflet coupling and inevitably is only of the order of nanometers, which explains the experimental result that fluctuations out of domain registry have not been observed by optical microscopy.
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Affiliation(s)
- G Garbès Putzel
- Department of Biomedical Engineering and Chemistry of Life Processes Institute, Northwestern University, Evanston, Illinois, USA
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15
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Jang HW, Felker DA, Bark CW, Wang Y, Niranjan MK, Nelson CT, Zhang Y, Su D, Folkman CM, Baek SH, Lee S, Janicka K, Zhu Y, Pan XQ, Fong DD, Tsymbal EY, Rzchowski MS, Eom CB. Metallic and Insulating Oxide Interfaces Controlled by Electronic Correlations. Science 2011; 331:886-9. [DOI: 10.1126/science.1198781] [Citation(s) in RCA: 193] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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16
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Dimensionality-driven insulator-metal transition in A-site excess non-stoichiometric perovskites. Nat Commun 2010; 1:106. [PMID: 21045824 PMCID: PMC3065906 DOI: 10.1038/ncomms1111] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2010] [Accepted: 10/07/2010] [Indexed: 11/08/2022] Open
Abstract
Coaxing correlated materials to the proximity of the insulator–metal transition region, where electronic wavefunctions transform from localized to itinerant, is currently the subject of intensive research because of the hopes it raises for technological applications and also for its fundamental scientific significance. In general, this tuning is achieved by either chemical doping to introduce charge carriers, or external stimuli to lower the ratio of Coulomb repulsion to bandwidth. In this study, we combine experiment and theory to show that the transition from well-localized insulating states to metallicity in a Ruddlesden-Popper series, La0.5Srn+1−0.5TinO3n+1, is driven by intercalating an intrinsically insulating SrTiO3 unit, in structural terms, by dimensionality n. This unconventional strategy, which can be understood upon a complex interplay between electron–phonon coupling and electron correlations, opens up a new avenue to obtain metallicity or even superconductivity in oxide superlattices that are normally expected to be insulators. Many technological applications would benefit from new ways of bringing complex materials near the insulator–metal transition region. The authors induce, in a Lantanum Strontium Titanate, a transition from insulating to metallic behaviour by structural intercalation of intrinsically insulating units, opening new avenues to engineer these materials.
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17
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Affiliation(s)
- J. Mannhart
- Center for Electronic Correlations and Magnetism, University of Augsburg, 86135 Augsburg, Germany
| | - D. G. Schlom
- Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853, USA
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18
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Pentcheva R, Pickett WE. Electronic phenomena at complex oxide interfaces: insights from first principles. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:043001. [PMID: 21386302 DOI: 10.1088/0953-8984/22/4/043001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Oxide interfaces have attracted considerable attention in recent years due to the emerging novel behavior which does not exist in the corresponding bulk parent compounds. This opens possibilities for future applications in oxide-based electronics and spintronics devices. Among the different materials combinations, heterostructures containing the two simple band insulators LaAlO(3) and SrTiO(3) have advanced to a model system exhibiting unanticipated properties ranging from conductivity, to magnetism, even to superconductivity. Electronic structure calculations have contributed significantly towards understanding these phenomena and we review here the progress achieved in the past few years, also showing some future directions and perspectives. A central issue in understanding the novel behavior in these oxide heterostructures is to discover the way (or ways) that these heterostructures deal with the polar discontinuity at the interface. Despite analogies to polar semiconductor interfaces, transition metal oxides offer much richer possibilities to compensate the valence mismatch, including, for example, an electronic reconstruction. Moreover, electronic correlations can lead to additional complex behavior like charge disproportionation and order, magnetism and orbital order. We discuss in some detail the role of finite size effects in ultrathin polar films on a nonpolar substrate leading to another intriguing feature-the thickness-dependent insulator-to-metal transition in thin LaAlO(3) films on a SrTiO(3)(001) substrate, driven by the impending polar catastrophe. The strong and uniform lattice polarization that emerges as a response to the potential build-up enables the system to remain insulating up to a few layers. However, beyond a critical thickness there is a crossover from an ionic relaxation to an electronic reconstruction. At this point two bands of electron and hole character, separated both in real and in reciprocal space, have been shifted sufficiently by the internal field in LaAlO(3) to impose the closing of the bandgap. We discuss briefly further parameters that allow one to manipulate this behavior, e.g. via vacancies, adsorbates or an oxide capping layer.
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Affiliation(s)
- Rossitza Pentcheva
- Department of Earth and Environmental Sciences, University of Munich, Munich, Germany
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19
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Sun CQ, Wang Y, Nie YG, Mehta BR, Khanuja M, Shivaprasad SM, Sun Y, Pan JS, Pan LK, Sun Z. Interface quantum trap depression and charge polarization in the CuPd and AgPd bimetallic alloy catalysts. Phys Chem Chem Phys 2010; 12:3131-5. [DOI: 10.1039/b922677j] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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20
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Niranjan MK, Wang Y, Jaswal SS, Tsymbal EY. Prediction of a switchable two-dimensional electron gas at ferroelectric oxide interfaces. PHYSICAL REVIEW LETTERS 2009; 103:016804. [PMID: 19659167 DOI: 10.1103/physrevlett.103.016804] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2009] [Indexed: 05/28/2023]
Abstract
The demonstration of a quasi-two-dimensional electron gas (2DEG) in LaAlO3/SrTiO3 heterostructures has stimulated intense research activity in recent years. The 2DEG has unique properties that are promising for applications in all-oxide electronic devices. For such applications it is desirable to have the ability to control 2DEG properties by external stimulus. Here, based on first-principles calculations we predict that all-oxide heterostructures incorporating ferroelectric constituents, such as KNbO3/ATiO3 (A=Sr, Ba, Pb), allow creating a 2DEG switchable between two conduction states by ferroelectric polarization reversal. The effect occurs due to the screening charge at the interface that counteracts the depolarizing electric field and depends on polarization orientation. The proposed concept of ferroelectrically controlled interface conductivity offers the possibility to design novel electronic devices.
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Affiliation(s)
- Manish K Niranjan
- Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, USA
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21
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Janicka K, Velev JP, Tsymbal EY. Quantum nature of two-dimensional electron gas confinement at LaAlO3/SrTiO3 interfaces. PHYSICAL REVIEW LETTERS 2009; 102:106803. [PMID: 19392142 DOI: 10.1103/physrevlett.102.106803] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2008] [Indexed: 05/27/2023]
Abstract
We perform density functional calculations to understand the mechanism controlling the confinement width of the two-dimensional electron gas (2DEG) at LaAlO_{3}/SrTiO_{3} interfaces. We find that the 2DEG confinement can be explained by the formation of metal induced gap states (MIGS) in the band gap of SrTiO3. These states are formed as the result of quantum-mechanical tunneling of the charge created at the interface due to electronic reconstruction. The attenuation length of the MIGS into the insulator is controlled by the lowest-decay-rate evanescent states of SrTiO3, as determined by its complex band structure. Our calculations predict that the 2DEG is confined in SrTiO3 within about 1 nm at the interface.
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Affiliation(s)
- Karolina Janicka
- Department of Physics, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, USA
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22
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Popović ZS, Satpathy S, Martin RM. Origin of the two-dimensional electron gas carrier density at the LaAlO3 on SrTiO3 interface. PHYSICAL REVIEW LETTERS 2008; 101:256801. [PMID: 19113736 DOI: 10.1103/physrevlett.101.256801] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2008] [Indexed: 05/27/2023]
Abstract
Transport measurements of the two-dimensional electron gas at the LaAlO3-SrTiO3 interface have found a density of carriers much lower than expected from the "polar catastrophe" arguments. From a detail density-functional study, we suggest how this discrepancy may be reconciled. We find that electrons occupy multiple subbands at the interface leading to a rich array of transport properties. Some electrons are confined to a single interfacial layer and susceptible to localization, while others with small masses and extended over several layers are expected to contribute to transport.
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Affiliation(s)
- Zoran S Popović
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801, USA
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23
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Nanda BRK, Satpathy S. Spin-polarized two-dimensional electron gas at oxide interfaces. PHYSICAL REVIEW LETTERS 2008; 101:127201. [PMID: 18851406 DOI: 10.1103/physrevlett.101.127201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2008] [Indexed: 05/26/2023]
Abstract
The possibility of formation of a fully spin-polarized 2D electron gas at the SrMnO_3/(LaMnO_3)_1/SrMnO_3 heterostructure is predicted from density-functional calculations. The La(d) electrons become confined in the direction normal to the interface in the electrostatic potential well of the positively charged layer of La atoms, acting as electron donors. These electrons mediate a ferromagnetic alignment of the Mn t_2g spins near the interface via Zener double exchange and become, in turn, spin-polarized due to the internal magnetic fields of the Mn moments.
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Affiliation(s)
- B R K Nanda
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
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24
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Pauli SA, Willmott PR. Conducting interfaces between polar and non-polar insulating perovskites. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2008; 20:264012. [PMID: 21694346 DOI: 10.1088/0953-8984/20/26/264012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Two-dimensional electron gases in semiconductors have found use in applications such as optoelectronics, high-power radio-frequency and magnetoelectronic devices. The ability to grow heterostructures of oxides exhibiting similar effects is a significant step towards the fabrication of all-oxide devices. Here, we give an overview of recent studies of two-dimensional electron gases formed at the interface between polar and non-polar perovskites. We discuss the proposed explanations of the origin of the conductivity and properties of the ground state.
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Affiliation(s)
- S A Pauli
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
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25
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Seo SSA, Choi WS, Lee HN, Yu L, Kim KW, Bernhard C, Noh TW. Optical study of the free-carrier response of LaTiO3/SrTiO3 superlattices. PHYSICAL REVIEW LETTERS 2007; 99:266801. [PMID: 18233598 DOI: 10.1103/physrevlett.99.266801] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2007] [Indexed: 05/25/2023]
Abstract
We used infrared spectroscopic ellipsometry to investigate the electronic properties of LaTiO_{3}/SrTiO_{3} superlattices (SLs). Our results indicated that, independent of the SL periodicity and individual layer thickness, the SLs exhibited a Drude metallic response with sheet carrier density per interface approximately 3x10;{14} cm;{-2}. This is probably due to the leakage of d electrons at interfaces from the Mott insulator LaTiO3 to the band insulator SrTiO3. We observed a carrier relaxation time approximately 35 fs and mobility approximately 35 cm;{2} V-1 s;{-1} at 10 K, and an unusual temperature dependence of carrier density that was attributed to the dielectric screening of quantum paraelectric SrTiO3.
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Affiliation(s)
- S S A Seo
- ReCOE & FPRD, Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
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26
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Pentcheva R, Pickett WE. Correlation-driven charge order at the interface between a Mott and a band insulator. PHYSICAL REVIEW LETTERS 2007; 99:016802. [PMID: 17678179 DOI: 10.1103/physrevlett.99.016802] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2006] [Indexed: 05/16/2023]
Abstract
To study digital Mott insulator LaTiO3 and band insulator SrTiO3 interfaces, we apply correlated band theory within the local density approximation including a Hubbard U to (n, m) multilayers, 1<or=n, m<or=9 using unit cells with larger lateral periodicity. If the on-site repulsion on Ti is big enough to model the Mott insulating behavior of undistorted LaTiO3, the charge imbalance at the interface is found in all cases to be accommodated by disproportionation (Ti4++Ti3+), charge ordering, and Ti3+ dxy-orbital ordering, with antiferromagnetic exchange coupling between the spins in the interface layer. Lattice relaxations lead to conducting behavior by shifting (slightly but importantly) the lower Hubbard band, but the charge and orbital order is robust against relaxation.
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Affiliation(s)
- Rossitza Pentcheva
- Department of Earth and Environmental Sciences, University of Munich, Theresienstrasse 41, 80333 Munich, Germany.
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27
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Fitting Kourkoutis L, Hotta Y, Susaki T, Hwang HY, Muller DA. Nanometer scale electronic reconstruction at the interface between LaVO3 and LaVO4. PHYSICAL REVIEW LETTERS 2006; 97:256803. [PMID: 17280379 DOI: 10.1103/physrevlett.97.256803] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2006] [Indexed: 05/13/2023]
Abstract
Electrons at interfaces, driven to minimize their free energy, are distributed differently than in bulk. This can be dramatic at interfaces involving heterovalent compounds. Here we profile an abrupt interface between V 3d2 LaVO3 and V 3d0 LaVO4 using electron energy loss spectroscopy. Although no bulk phase of LaVOx with a V 3d1 configuration exists, we find a nanometer-wide region of V 3d1 at the LaVO3/LaVO4 interface, rather than a mixture of V 3d0 and V 3d2. The two-dimensional sheet of 3d1 electrons is a prototypical electronic reconstruction at an interface between competing ground states.
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Affiliation(s)
- L Fitting Kourkoutis
- School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
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28
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Okamoto S, Millis AJ, Spaldin NA. Lattice relaxation in oxide heterostructures: LaTiO3/SrTiO3 superlattices. PHYSICAL REVIEW LETTERS 2006; 97:056802. [PMID: 17026128 DOI: 10.1103/physrevlett.97.056802] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2006] [Indexed: 05/12/2023]
Abstract
Local density approximation + Hubbard U and many-body effective Hamiltonian calculations are used to determine the effects of lattice relaxation in LaTiO3/SrTiO3 superlattices. Large ferroelectric-like distortions of the TiO6 octahedra are found, which substantially affect the Ti d-electron density, bringing the calculated results into good agreement with experimental data. The relaxations also change the many-body physics, leading to a novel symmetry-breaking-induced ordering of the xy orbitals, which does not occur in bulk LaTiO3, or in the hypothetical unrelaxed structure.
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Affiliation(s)
- Satoshi Okamoto
- Department of Physics, Columbia University, 538 West 120th Street, New York, NY 10027, USA.
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29
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Takizawa M, Wadati H, Tanaka K, Hashimoto M, Yoshida T, Fujimori A, Chikamatsu A, Kumigashira H, Oshima M, Shibuya K, Mihara T, Ohnishi T, Lippmaa M, Kawasaki M, Koinuma H, Okamoto S, Millis AJ. Photoemission from buried interfaces in SrTiO3/LaTiO3 superlattices. PHYSICAL REVIEW LETTERS 2006; 97:057601. [PMID: 17026141 DOI: 10.1103/physrevlett.97.057601] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2006] [Indexed: 05/12/2023]
Abstract
We have measured photoemission spectra of SrTiO3/LaTiO3 superlattices with a topmost SrTiO3 layer of variable thickness. A finite coherent spectral weight with a clear Fermi cutoff was observed at chemically abrupt SrTiO3/LaTiO3 interfaces, indicating that an "electronic reconstruction" occurs at the interface between the Mott insulator LaTiO3 and the band insulator SrTiO3. For SrTiO3/LaTiO3 interfaces annealed at high temperatures (approximately 1000 degrees C), which leads to Sr/La atomic interdiffusion and hence to the formation of La(1-x)Sr(x)TiO3-like material, the intensity of the incoherent part was found to be dramatically reduced whereas the coherent part with a sharp Fermi cutoff was enhanced due to the spread of charge. These important experimental features are well reproduced by layer dynamical-mean-field-theory calculation.
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Affiliation(s)
- M Takizawa
- Department of Physics and Department of Complexity Science and Engineering, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwashi, Chiba 277-8561, Japan
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