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Yuan Y, Patel RK, Banik S, Reta TB, Bisht RS, Fong DD, Sankaranarayanan SKRS, Ramanathan S. Proton Conducting Neuromorphic Materials and Devices. Chem Rev 2024. [PMID: 39038231 DOI: 10.1021/acs.chemrev.4c00071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/24/2024]
Abstract
Neuromorphic computing and artificial intelligence hardware generally aims to emulate features found in biological neural circuit components and to enable the development of energy-efficient machines. In the biological brain, ionic currents and temporal concentration gradients control information flow and storage. It is therefore of interest to examine materials and devices for neuromorphic computing wherein ionic and electronic currents can propagate. Protons being mobile under an external electric field offers a compelling avenue for facilitating biological functionalities in artificial synapses and neurons. In this review, we first highlight the interesting biological analog of protons as neurotransmitters in various animals. We then discuss the experimental approaches and mechanisms of proton doping in various classes of inorganic and organic proton-conducting materials for the advancement of neuromorphic architectures. Since hydrogen is among the lightest of elements, characterization in a solid matrix requires advanced techniques. We review powerful synchrotron-based spectroscopic techniques for characterizing hydrogen doping in various materials as well as complementary scattering techniques to detect hydrogen. First-principles calculations are then discussed as they help provide an understanding of proton migration and electronic structure modification. Outstanding scientific challenges to further our understanding of proton doping and its use in emerging neuromorphic electronics are pointed out.
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Affiliation(s)
- Yifan Yuan
- Department of Electrical & Computer Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
| | - Ranjan Kumar Patel
- Department of Electrical & Computer Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
| | - Suvo Banik
- Department of Mechanical and Industrial Engineering, University of Illinois, Chicago, Illinois 60607, United States
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Tadesse Billo Reta
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Ravindra Singh Bisht
- Department of Electrical & Computer Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
| | - Dillon D Fong
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Subramanian K R S Sankaranarayanan
- Department of Mechanical and Industrial Engineering, University of Illinois, Chicago, Illinois 60607, United States
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Shriram Ramanathan
- Department of Electrical & Computer Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
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2
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Park TJ, Deng S, Manna S, Islam ANMN, Yu H, Yuan Y, Fong DD, Chubykin AA, Sengupta A, Sankaranarayanan SKRS, Ramanathan S. Complex Oxides for Brain-Inspired Computing: A Review. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2203352. [PMID: 35723973 DOI: 10.1002/adma.202203352] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 06/02/2022] [Indexed: 06/15/2023]
Abstract
The fields of brain-inspired computing, robotics, and, more broadly, artificial intelligence (AI) seek to implement knowledge gleaned from the natural world into human-designed electronics and machines. In this review, the opportunities presented by complex oxides, a class of electronic ceramic materials whose properties can be elegantly tuned by doping, electron interactions, and a variety of external stimuli near room temperature, are discussed. The review begins with a discussion of natural intelligence at the elementary level in the nervous system, followed by collective intelligence and learning at the animal colony level mediated by social interactions. An important aspect highlighted is the vast spatial and temporal scales involved in learning and memory. The focus then turns to collective phenomena, such as metal-to-insulator transitions (MITs), ferroelectricity, and related examples, to highlight recent demonstrations of artificial neurons, synapses, and circuits and their learning. First-principles theoretical treatments of the electronic structure, and in situ synchrotron spectroscopy of operating devices are then discussed. The implementation of the experimental characteristics into neural networks and algorithm design is then revewed. Finally, outstanding materials challenges that require a microscopic understanding of the physical mechanisms, which will be essential for advancing the frontiers of neuromorphic computing, are highlighted.
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Affiliation(s)
- Tae Joon Park
- School of Materials Engineering, Purdue University, West Lafayette, IN, 47907, USA
| | - Sunbin Deng
- School of Materials Engineering, Purdue University, West Lafayette, IN, 47907, USA
| | - Sukriti Manna
- Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL, 60439, USA
| | - A N M Nafiul Islam
- Department of Electrical Engineering, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Haoming Yu
- School of Materials Engineering, Purdue University, West Lafayette, IN, 47907, USA
| | - Yifan Yuan
- School of Materials Engineering, Purdue University, West Lafayette, IN, 47907, USA
| | - Dillon D Fong
- Materials Science Division, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Alexander A Chubykin
- Department of Biological Sciences, Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN, 47907, USA
| | - Abhronil Sengupta
- Department of Electrical Engineering, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Subramanian K R S Sankaranarayanan
- Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL, 60439, USA
- Department of Mechanical and Industrial Engineering, University of Illinois Chicago, Chicago, IL, 60607, USA
| | - Shriram Ramanathan
- School of Materials Engineering, Purdue University, West Lafayette, IN, 47907, USA
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3
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Jia T, Chen Z, Rebec SN, Hashimoto M, Lu D, Devereaux TP, Lee D, Moore RG, Shen Z. Magic Doping and Robust Superconductivity in Monolayer FeSe on Titanates. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2021; 8:2003454. [PMID: 33977049 PMCID: PMC8097367 DOI: 10.1002/advs.202003454] [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: 09/10/2020] [Revised: 01/11/2021] [Indexed: 06/12/2023]
Abstract
The enhanced superconductivity in monolayer FeSe on titanates opens a fascinating pathway toward the rational design of high-temperature superconductors. Utilizing the state-of-the-art oxide plus chalcogenide molecular beam epitaxy systems in situ connected to a synchrotron angle-resolved photoemission spectroscope, epitaxial LaTiO3 layers with varied atomic thicknesses are inserted between monolayer FeSe and SrTiO3, for systematic modulation of interfacial chemical potential. With the dramatic increase of electron accumulation at the LaTiO3/SrTiO3 surface, providing a substantial surge of work function mismatch across the FeSe/oxide interface, the charge transfer and the superconducting gap in the monolayer FeSe are found to remain markedly robust. This unexpected finding indicate the existence of an intrinsically anchored "magic" doping within the monolayer FeSe systems.
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Affiliation(s)
- Tao Jia
- Stanford Institute for Materials and Energy SciencesSLAC National Accelerator LaboratoryMenlo ParkCA94025USA
- Departments of Physics, Applied Physics, and Materials Science and EngineeringGeballe Laboratory for Advanced MaterialsStanford UniversityStanfordCA94305USA
| | - Zhuoyu Chen
- Stanford Institute for Materials and Energy SciencesSLAC National Accelerator LaboratoryMenlo ParkCA94025USA
- Departments of Physics, Applied Physics, and Materials Science and EngineeringGeballe Laboratory for Advanced MaterialsStanford UniversityStanfordCA94305USA
| | - Slavko N. Rebec
- Stanford Institute for Materials and Energy SciencesSLAC National Accelerator LaboratoryMenlo ParkCA94025USA
- Departments of Physics, Applied Physics, and Materials Science and EngineeringGeballe Laboratory for Advanced MaterialsStanford UniversityStanfordCA94305USA
| | - Makoto Hashimoto
- Stanford Synchrotron Radiation LightsourceSLAC National Accelerator LaboratoryMenlo ParkCA94025USA
| | - Donghui Lu
- Stanford Synchrotron Radiation LightsourceSLAC National Accelerator LaboratoryMenlo ParkCA94025USA
| | - Thomas P. Devereaux
- Stanford Institute for Materials and Energy SciencesSLAC National Accelerator LaboratoryMenlo ParkCA94025USA
- Departments of Physics, Applied Physics, and Materials Science and EngineeringGeballe Laboratory for Advanced MaterialsStanford UniversityStanfordCA94305USA
| | - Dung‐Hai Lee
- Department of PhysicsUniversity of California at BerkeleyBerkeleyCA94720USA
- Materials Sciences DivisionLawrence Berkeley National LaboratoryBerkeleyCA94720USA
| | - Robert G. Moore
- Materials Science and Technology DivisionOak Ridge National LaboratoryOak RidgeTN37831USA
| | - Zhi‐Xun Shen
- Stanford Institute for Materials and Energy SciencesSLAC National Accelerator LaboratoryMenlo ParkCA94025USA
- Departments of Physics, Applied Physics, and Materials Science and EngineeringGeballe Laboratory for Advanced MaterialsStanford UniversityStanfordCA94305USA
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4
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Cook S, Letchworth-Weaver K, Tung IC, Andersen TK, Hong H, Marks LD, Fong DD. How heteroepitaxy occurs on strontium titanate. SCIENCE ADVANCES 2019; 5:eaav0764. [PMID: 30993200 PMCID: PMC6461459 DOI: 10.1126/sciadv.aav0764] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2018] [Accepted: 02/14/2019] [Indexed: 06/01/2023]
Abstract
In traditional models of heteroepitaxy, the substrate serves mainly as a crystalline template for the thin-film lattice, dictating the initial roughness of the film and the degree of coherent strain. Here, performing in situ surface x-ray diffraction during the heteroepitaxial growth of LaTiO3 on SrTiO3 (001), we find that a TiO2 adlayer composed of the ( 13 × 13 ) R33.7° and ( 2 × 2 ) R45.0° reconstructions is a highly active participant in the growth process, continually diffusing to the surface throughout deposition. The effects of the TiO2 adlayer on layer-by-layer growth are investigated using different deposition sequences and anomalous x-ray scattering, both of which permit detailed insight into the dynamic layer rearrangements that take place. Our work challenges commonly held assumptions regarding growth on TiO2-terminated SrTiO3 (001) and demonstrates the critical role of excess TiO2 surface stoichiometry on the initial stages of heteroepitaxial growth on this important perovskite oxide substrate material.
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Affiliation(s)
- Seyoung Cook
- Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60202, USA
| | | | - I-Cheng Tung
- X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Tassie K. Andersen
- Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60202, USA
| | - Hawoong Hong
- X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Laurence D. Marks
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60202, USA
| | - Dillon D. Fong
- Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
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5
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Zhu J, Lee JW, Lee H, Xie L, Pan X, De Souza RA, Eom CB, Nonnenmann SS. Probing vacancy behavior across complex oxide heterointerfaces. SCIENCE ADVANCES 2019; 5:eaau8467. [PMID: 30801011 PMCID: PMC6386560 DOI: 10.1126/sciadv.aau8467] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 01/11/2019] [Indexed: 06/09/2023]
Abstract
Oxygen vacancies ( V O • • ) play a critical role as defects in complex oxides in establishing functionality in systems including memristors, all-oxide electronics, and electrochemical cells that comprise metal-insulator-metal or complex oxide heterostructure configurations. Improving oxide-oxide interfaces necessitates a direct, spatial understanding of vacancy distributions that define electrochemically active regions. We show vacancies deplete over micrometer-level distances in Nb-doped SrTiO3 (Nb:SrTiO3) substrates due to deposition and post-annealing processes. We convert the surface potential across a strontium titanate/yttria-stabilized zirconia (STO/YSZ) heterostructured film to spatial (<100 nm) vacancy profiles within STO using (T = 500°C) in situ scanning probes and semiconductor analysis. Oxygen scavenging occurring during pulsed laser deposition reduces Nb:STO substantially, which partially reoxidizes in an oxygen-rich environment upon cooling. These results (i) introduce the means to spatially resolve quantitative vacancy distributions across oxide films and (ii) indicate the mechanisms by which oxide thin films enhance and then deplete vacancies within the underlying substrate.
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Affiliation(s)
- Jiaxin Zhu
- Department of Mechanical and Industrial Engineering, University of Massachusetts-Amherst, Amherst, MA 01003, USA
| | - Jung-Woo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Hyungwoo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Lin Xie
- Department of Chemical Engineering and Materials Science, University of California, Irvine, Irvine, CA 92697, USA
| | - Xiaoqing Pan
- Department of Chemical Engineering and Materials Science, University of California, Irvine, Irvine, CA 92697, USA
| | - Roger A. De Souza
- Institute of Physical Chemistry, RWTH Aachen University, Aachen 52056, Germany
| | - Chang-Beom Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Stephen S. Nonnenmann
- Department of Mechanical and Industrial Engineering, University of Massachusetts-Amherst, Amherst, MA 01003, USA
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6
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Chikina A, Lechermann F, Husanu MA, Caputo M, Cancellieri C, Wang X, Schmitt T, Radovic M, Strocov VN. Orbital Ordering of the Mobile and Localized Electrons at Oxygen-Deficient LaAlO 3/SrTiO 3 Interfaces. ACS NANO 2018; 12:7927-7935. [PMID: 29995384 DOI: 10.1021/acsnano.8b02335] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Interfacing different transition-metal oxides opens a route to functionalizing their rich interplay of electron, spin, orbital, and lattice degrees of freedom for electronic and spintronic devices. Electronic and magnetic properties of SrTiO3-based interfaces hosting a mobile two-dimensional electron system (2DES) are strongly influenced by oxygen vacancies, which form an electronic dichotomy, where strongly correlated localized electrons in the in-gap states (IGSs) coexist with noncorrelated delocalized 2DES. Here, we use resonant soft-X-ray photoelectron spectroscopy to prove the eg character of the IGSs, as opposed to the t2g character of the 2DES in the paradigmatic LaAlO3/SrTiO3 interface. We furthermore separate the d xy and d xz/d xz orbital contributions based on deeper consideration of the resonant photoexcitation process in terms of orbital and momentum selectivity. Supported by a self-consistent combination of density functional theory and dynamical mean field theory calculations, this experiment identifies local orbital reconstruction that goes beyond the conventional eg- vs-t2g band ordering. A hallmark of oxygen-deficient LaAlO3/SrTiO3 is a significant hybridization of the eg and t2g orbitals. Our findings provide routes for tuning the electronic and magnetic properties of oxide interfaces through "defect engineering" with oxygen vacancies.
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Affiliation(s)
- Alla Chikina
- Swiss Light Source, Paul Scherrer Institute , Villigen CH-5232 , Switzerland
| | - Frank Lechermann
- Institut für Theoretische Physik , Universität Hamburg , Jungiusstrasse 9 , Hamburg DE-20355 , Germany
| | - Marius-Adrian Husanu
- Swiss Light Source, Paul Scherrer Institute , Villigen CH-5232 , Switzerland
- National Institute of Materials Physics , Atomistilor 405A , Magurele RO-077125 , Romania
| | - Marco Caputo
- Swiss Light Source, Paul Scherrer Institute , Villigen CH-5232 , Switzerland
| | - Claudia Cancellieri
- Swiss Light Source, Paul Scherrer Institute , Villigen CH-5232 , Switzerland
- Empa, Swiss Federal Laboratories for Materials Science & Technology , Ueberlandstrasse 129 , Duebendorf CH-8600 , Switzerland
| | - Xiaoqiang Wang
- Swiss Light Source, Paul Scherrer Institute , Villigen CH-5232 , Switzerland
| | - Thorsten Schmitt
- Swiss Light Source, Paul Scherrer Institute , Villigen CH-5232 , Switzerland
| | - Milan Radovic
- Swiss Light Source, Paul Scherrer Institute , Villigen CH-5232 , Switzerland
| | - Vladimir N Strocov
- Swiss Light Source, Paul Scherrer Institute , Villigen CH-5232 , Switzerland
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7
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Scheiderer P, Schmitt M, Gabel J, Zapf M, Stübinger M, Schütz P, Dudy L, Schlueter C, Lee TL, Sing M, Claessen R. Tailoring Materials for Mottronics: Excess Oxygen Doping of a Prototypical Mott Insulator. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1706708. [PMID: 29732633 DOI: 10.1002/adma.201706708] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Revised: 02/02/2018] [Indexed: 06/08/2023]
Abstract
The Mott transistor is a paradigm for a new class of electronic devices-often referred to by the term Mottronics-which are based on charge correlations between the electrons. Since correlation-induced insulating phases of most oxide compounds are usually very robust, new methods have to be developed to push such materials right to the boundary to the metallic phase in order to enable the metal-insulator transition to be switched by electric gating. Here, it is demonstrated that thin films of the prototypical Mott insulator LaTiO3 grown by pulsed laser deposition under oxygen atmosphere are readily tuned by excess oxygen doping across the line of the band-filling controlled Mott transition in the electronic phase diagram. The detected insulator to metal transition is characterized by a strong change in resistivity of several orders of magnitude. The use of suitable substrates and capping layers to inhibit oxygen diffusion facilitates full control of the oxygen content and renders the films stable against exposure to ambient conditions. These achievements represent a significant advancement in control and tuning of the electronic properties of LaTiO3+x thin films making it a promising channel material in future Mottronic devices.
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Affiliation(s)
- Philipp Scheiderer
- Physikalisches Institut and Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Matthias Schmitt
- Physikalisches Institut and Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Judith Gabel
- Physikalisches Institut and Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Michael Zapf
- Physikalisches Institut and Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Martin Stübinger
- Physikalisches Institut and Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Philipp Schütz
- Physikalisches Institut and Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Lenart Dudy
- Physikalisches Institut and Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | | | - Tien-Lin Lee
- Diamond Light Source Ltd., Didcot, Oxfordshire, OX11 0DE, UK
| | - Michael Sing
- Physikalisches Institut and Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Ralph Claessen
- Physikalisches Institut and Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
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8
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Palina N, Annadi A, Asmara TC, Diao C, Yu X, Breese MBH, Venkatesan T, Ariando A, Rusydi A. Electronic defect states at the LaAlO3/SrTiO3 heterointerface revealed by O K-edge X-ray absorption spectroscopy. Phys Chem Chem Phys 2016; 18:13844-51. [DOI: 10.1039/c6cp00028b] [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
Interfaces of two dissimilar complex oxides exhibit exotic physical properties that are absent in their parent compounds.
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Affiliation(s)
- Natalia Palina
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
- NUSNNI-Nanocore
| | - Anil Annadi
- NUSNNI-Nanocore
- National University of Singapore
- Singapore 117411
- Singapore
- Department of Physics and Astronomy
| | - Teguh Citra Asmara
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
- NUSNNI-Nanocore
| | - Caozheng Diao
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
| | - Xiaojiang Yu
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
| | - Mark B. H. Breese
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
- Department of Physics
| | - T. Venkatesan
- NUSNNI-Nanocore
- National University of Singapore
- Singapore 117411
- Singapore
- Department of Physics
| | - Ariando Ariando
- NUSNNI-Nanocore
- National University of Singapore
- Singapore 117411
- Singapore
- Department of Physics
| | - Andrivo Rusydi
- Singapore Synchrotron Light Source
- National University of Singapore
- Singapore 117603
- Singapore
- NUSNNI-Nanocore
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9
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Jilili J, Cossu F, Schwingenschlögl U. Trends in (LaMnO3)n/(SrTiO3)m superlattices with varying layer thicknesses. Sci Rep 2015; 5:13762. [PMID: 26323361 PMCID: PMC4555181 DOI: 10.1038/srep13762] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2015] [Accepted: 08/04/2015] [Indexed: 11/09/2022] Open
Abstract
We investigate the thickness dependence of the structural, electronic, and magnetic properties of (LaMnO3)n/(SrTiO3)m (n, m = 2, 4, 6, 8) superlattices using density functional theory. The electronic structure turns out to be highly sensitive to the onsite Coulomb interaction. In contrast to bulk SrTiO3, strongly distorted O octahedra are observed in the SrTiO3 layers with a systematic off centering of the Ti atoms. The systems favour ferromagnetic spin ordering rather than the antiferromagnetic spin ordering of bulk LaMnO3 and all show half-metallicity, while a systematic reduction of the minority spin band gaps as a function of the LaMnO3 and SrTiO3 layer thicknesses originates from modifications of the Ti dxy states.
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Affiliation(s)
- J Jilili
- KAUST, PSE Division, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - F Cossu
- KAUST, PSE Division, Thuwal 23955-6900, Kingdom of Saudi Arabia
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10
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Kleibeuker JE, Zhong Z, Nishikawa H, Gabel J, Müller A, Pfaff F, Sing M, Held K, Claessen R, Koster G, Rijnders G. Electronic reconstruction at the isopolar LaTiO(3)/LaFeO(3) interface: an X-ray photoemission and density-functional theory study. PHYSICAL REVIEW LETTERS 2014; 113:237402. [PMID: 25526156 DOI: 10.1103/physrevlett.113.237402] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Indexed: 06/04/2023]
Abstract
We report the formation of a nonmagnetic band insulator at the isopolar interface between the antiferromagnetic Mott-Hubbard insulator LaTiO_{3} and the antiferromagnetic charge transfer insulator LaFeO_{3}. By density-functional theory calculations, we find that the formation of this interface state is driven by the combination of O band alignment and crystal field splitting energy of the t_{2g} and e_{g} bands. As a result of these two driving forces, the Fe 3d bands rearrange and electrons are transferred from Ti to Fe. This picture is supported by x-ray photoelectron spectroscopy, which confirms the rearrangement of the Fe 3d bands and reveals an unprecedented charge transfer up to 1.2±0.2 e^{-}/interface unit cell in our LaTiO_{3}/LaFeO_{3} heterostructures.
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Affiliation(s)
- J E Kleibeuker
- Faculty of Science and Technology and MESA+Institute for Nanotechnology, University of Twente, 7500 AE Enschede, Netherlands and Physikalisches Institut, University of Würzburg, 97074 Würzburg, Germany
| | - Z Zhong
- Institute of Solid State Physics, Vienna University of Technology, A-1040 Vienna, Austria
| | - H Nishikawa
- Faculty of Biology-Oriented Science and Technology, Kinki University, Kinokawa 649-6493, Japan
| | - J Gabel
- Physikalisches Institut, University of Würzburg, 97074 Würzburg, Germany
| | - A Müller
- Physikalisches Institut, University of Würzburg, 97074 Würzburg, Germany
| | - F Pfaff
- Physikalisches Institut, University of Würzburg, 97074 Würzburg, Germany
| | - M Sing
- Physikalisches Institut, University of Würzburg, 97074 Würzburg, Germany
| | - K Held
- Institute of Solid State Physics, Vienna University of Technology, A-1040 Vienna, Austria
| | - R Claessen
- Physikalisches Institut, University of Würzburg, 97074 Würzburg, Germany
| | - G Koster
- Faculty of Science and Technology and MESA+Institute for Nanotechnology, University of Twente, 7500 AE Enschede, Netherlands
| | - G Rijnders
- Faculty of Science and Technology and MESA+Institute for Nanotechnology, University of Twente, 7500 AE Enschede, Netherlands
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11
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Salman Z, Prokscha T, Amato A, Morenzoni E, Scheuermann R, Sedlak K, Suter A. Direct spectroscopic observation of a shallow hydrogenlike donor state in insulating SrTiO3. PHYSICAL REVIEW LETTERS 2014; 113:156801. [PMID: 25375730 DOI: 10.1103/physrevlett.113.156801] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Indexed: 06/04/2023]
Abstract
We present a direct spectroscopic observation of a shallow hydrogenlike muonium state in SrTiO(3) which confirms the theoretical prediction that interstitial hydrogen may act as a shallow donor in this material. The formation of this muonium state is temperature dependent and appears below ∼ 70K. From the temperature dependence we estimate an activation energy of ∼ 50 meV in the bulk and ∼ 23 meV near the free surface. The field and directional dependence of the muonium precession frequencies further supports the shallow impurity state with a rare example of a fully anisotropic hyperfine tensor. From these measurements we determine the strength of the hyperfine interaction and propose that the muon occupies an interstitial site near the face of the oxygen octahedron in SrTiO(3). The observed shallow donor state provides new insight for tailoring the electronic and optical properties of SrTiO(3)-based oxide interface systems.
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Affiliation(s)
- Z Salman
- Paul Scherrer Institute, Laboratory for Muon Spin Spectroscopy, CH-5232 Villigen PSI, Switzerland
| | - T Prokscha
- Paul Scherrer Institute, Laboratory for Muon Spin Spectroscopy, CH-5232 Villigen PSI, Switzerland
| | - A Amato
- Paul Scherrer Institute, Laboratory for Muon Spin Spectroscopy, CH-5232 Villigen PSI, Switzerland
| | - E Morenzoni
- Paul Scherrer Institute, Laboratory for Muon Spin Spectroscopy, CH-5232 Villigen PSI, Switzerland
| | - R Scheuermann
- Paul Scherrer Institute, Laboratory for Muon Spin Spectroscopy, CH-5232 Villigen PSI, Switzerland
| | - K Sedlak
- Paul Scherrer Institute, Laboratory for Muon Spin Spectroscopy, CH-5232 Villigen PSI, Switzerland
| | - A Suter
- Paul Scherrer Institute, Laboratory for Muon Spin Spectroscopy, CH-5232 Villigen PSI, Switzerland
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12
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Suppression of the two-dimensional electron gas in LaGaO3/SrTiO3 by cation intermixing. Sci Rep 2013; 3:3409. [PMID: 24296477 PMCID: PMC3847700 DOI: 10.1038/srep03409] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Accepted: 11/18/2013] [Indexed: 11/09/2022] Open
Abstract
Cation intermixing at the n-type polar LaGaO3/SrTiO3 (001) interface is investigated by first principles calculations. Ti⇔Ga, Sr⇔La, and SrTi⇔LaGa intermixing are studied in comparison to each other, with a focus on the interface stability. We demonstrate in which cases intermixing is energetically favorable as compared to a clean interface. A depopulation of the Ti 3dxy orbitals under cation intermixing is found, reflecting a complete suppression of the two-dimensional electron gas present at the clean interface.
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13
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Chang YJ, Moreschini L, Bostwick A, Gaines GA, Kim YS, Walter AL, Freelon B, Tebano A, Horn K, Rotenberg E. Layer-by-layer evolution of a two-dimensional electron gas near an oxide interface. PHYSICAL REVIEW LETTERS 2013; 111:126401. [PMID: 24093281 DOI: 10.1103/physrevlett.111.126401] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Indexed: 06/02/2023]
Abstract
We report the momentum-resolved measurement of a two-dimensional electron gas at the LaTiO(3)/SrTiO(3) interface by angle-resolved photoemission spectroscopy (ARPES). Thanks to an advanced sample preparation technique, the orbital character of the conduction electrons and the electronic correlations can be accessed quantitatively as each unit cell layer is added. We find that all of these quantities change dramatically with distance from the interface. These findings open the way to analogous studies on other heterostructures, which are traditionally a forbidden field for ARPES.
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Affiliation(s)
- Young Jun Chang
- Advanced Light Source (ALS), E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA and Department of Physical Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany and Department of Physics, University of Seoul, Seoul 130-743, Korea
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14
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Cancellieri C, Reinle-Schmitt ML, Kobayashi M, Strocov VN, Schmitt T, Willmott PR, Gariglio S, Triscone JM. Interface Fermi states of LaAlO3/SrTiO3 and related heterostructures. PHYSICAL REVIEW LETTERS 2013; 110:137601. [PMID: 23581372 DOI: 10.1103/physrevlett.110.137601] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Indexed: 06/02/2023]
Abstract
The interfaces of LaAlO3/SrTiO3 and (LaAlO3)(x)(SrTiO3)(1-x)/SrTiO3 heterostructures have been investigated by soft x-ray photoelectron spectroscopy for different layer thicknesses across the insulator-to-metal interface transition. The valence band and Fermi edge were probed using resonant photoemission across the Ti L(2,3) absorption edge. The presence of a Fermi-edge signal originating from the partially filled Ti 3d orbitals is only found in the conducting samples. No Fermi-edge signal could be detected for insulating samples below the critical thickness. Furthermore, the angular dependence of the Fermi intensity allows the determination of the spatial extent of the conducting electron density perpendicular to the interface.
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Affiliation(s)
- C Cancellieri
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland.
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15
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Drera G, Sangaletti L, Bondino F, Malvestuto M, Malavasi L, Diaz-Fernandez Y, Dash S, Mozzati MC, Galinetto P. Labeling interacting configurations through an analysis of excitation dynamics in a resonant photoemission experiment: the case of rutile TiO2. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:075502. [PMID: 23328648 DOI: 10.1088/0953-8984/25/7/075502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
A detailed study of resonant photoemission at Ti L(2,3) edges of insulating rutile TiO(2-x) thin film is presented. Pure TiO(2) resonating structures, defect-related resonances, resonant Raman-Auger and normal LVV Auger emissions are tracked, including an unpredicted two-hole correlated satellite below the non-bonding part of the valence band. The analysis of excitation dynamics unambiguously addresses the origin of these features and, in particular, the extent of charge transfer effects on the Ti-O bonding in the valence band of rutile, disclosing further applications to the more general case of, formally, d(0) oxides.
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Affiliation(s)
- G Drera
- Interdisciplinary Laboratories for Advanced Materials Physics, I-LAMP, and Dipartimento di Matematica e Fisica, Università Cattolica, Via dei Musei 41, I-25121, Brescia, Italy
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16
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Salman Z, Ofer O, Radovic M, Hao H, Ben Shalom M, Chow KH, Dagan Y, Hossain MD, Levy CDP, Macfarlane WA, Morris GM, Patthey L, Pearson MR, Saadaoui H, Schmitt T, Wang D, Kiefl RF. Nature of weak magnetism in SrTiO3/LaAlO3 multilayers. PHYSICAL REVIEW LETTERS 2012; 109:257207. [PMID: 23368496 DOI: 10.1103/physrevlett.109.257207] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2012] [Revised: 09/20/2012] [Indexed: 06/01/2023]
Abstract
We report the observation of weak magnetism in superlattices of LaAlO(3)/SrTiO(3) using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of ^{8}Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO(3) exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO(3)/SrTiO(3) interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ~4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (~0.002μ(B)) in the two samples with a larger LaAlO(3) spacer thickness.
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Affiliation(s)
- Z Salman
- Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
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17
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Wadati H, Geck J, Hawthorn DG, Higuchi T, Hosoda M, Bell C, Hikita Y, Hwang HY, Schussler-Langeheine C, Schierle E, Weschke E, Sawatzky GA. Electronic structure of the SrTiO3/LaAlO3interface revealed by resonant soft x-ray scattering. ACTA ACUST UNITED AC 2011. [DOI: 10.1088/1757-899x/24/1/012012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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18
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Biscaras J, Bergeal N, Kushwaha A, Wolf T, Rastogi A, Budhani R, Lesueur J. Two-dimensional superconductivity at a Mott insulator/band insulator interface LaTiO3/SrTiO3. Nat Commun 2010; 1:89. [DOI: 10.1038/ncomms1084] [Citation(s) in RCA: 221] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Accepted: 09/06/2010] [Indexed: 11/09/2022] Open
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19
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Shah AB, Ramasse QM, Zhai X, Wen JG, May SJ, Petrov I, Bhattacharya A, Abbamonte P, Eckstein JN, Zuo JM. Probing interfacial electronic structures in atomic layer LaMnO(3) and SrTiO(3) superlattices. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2010; 22:1156-1160. [PMID: 20401940 DOI: 10.1002/adma.200904198] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Affiliation(s)
- Amish B Shah
- Department of Materials Science and Engineering and Fredrick Seitz Materials Research Laboratory University of Illinois at Urbana-Champaign Urbana, Illinois 61801, USA
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20
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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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21
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Garcia-Barriocanal J, Bruno FY, Rivera-Calzada A, Sefrioui Z, Nemes NM, Garcia-Hernández M, Rubio-Zuazo J, Castro GR, Varela M, Pennycook SJ, Leon C, Santamaria J. "Charge leakage" at LaMnO3/SrTiO3 interfaces. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2010; 22:627-632. [PMID: 20217762 DOI: 10.1002/adma.200902263] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
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22
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Chambers SA. Epitaxial growth and properties of doped transition metal and complex oxide films. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2010; 22:219-248. [PMID: 20217685 DOI: 10.1002/adma.200901867] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The detailed science and technology of crystalline oxide film growth using vacuum methods is reviewed and discussed with an eye toward gaining fundamental insights into the relationships between growth process and parameters, film and interface structure and composition, and electronic, magnetic and photochemical properties. The topic is approached first from a comparative point of view based on the most widely used growth methods, and then on the basis of specific material systems that have generated very high levels of interest. Emphasis is placed on the wide diversity of structural, electronic, optical and magnetic properties exhibited by oxides, and the fascinating results that this diversity of properties can produce when combined with the degrees of freedom afforded by heteroepitaxy.
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Affiliation(s)
- Scott A Chambers
- Chemical and Materials Science Division, Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, PO Box 999, MS K8-87, Richland, WA 99352, USA.
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23
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Takizawa M, Hotta Y, Susaki T, Ishida Y, Wadati H, Takata Y, Horiba K, Matsunami M, Shin S, Yabashi M, Tamasaku K, Nishino Y, Ishikawa T, Fujimori A, Hwang HY. Spectroscopic evidence for competing reconstructions in polar multilayers LaAlO3/LaVO3/LaAlO3. PHYSICAL REVIEW LETTERS 2009; 102:236401. [PMID: 19658952 DOI: 10.1103/physrevlett.102.236401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2008] [Indexed: 05/28/2023]
Abstract
We have studied the valence redistribution of V in LaAlO(3)/LaVO(3)/LaAlO(3) trilayers, which are composed of only polar layers grown on SrTiO3 (001) substrates, by core-level photoemission spectroscopy. We have found that the V valence is intermediate between V3+ and V4+ for thin LaAlO3 cap layers, decreases with increasing cap-layer thickness, and finally recovers the bulk value of V3+ at approximately 10 unit-cell thickness. In order to interpret these results, we propose that the atomic reconstruction of the polar LaAlO3 surface competes with the purely electronic V valence change so that the polar catastrophe is avoided at the cost of minimum energy.
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Affiliation(s)
- M Takizawa
- Department of Physics, University of Tokyo, 3-7-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
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24
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Ou HW, Zhao JF, Zhang Y, Xie BP, Shen DW, Zhu Y, Yang ZQ, Che JG, Luo XG, Chen XH, Arita M, Shimada K, Namatame H, Taniguchi M, Cheng CM, Tsuei KD, Feng DL. Novel electronic structure induced by a highly strained oxide interface with incommensurate crystal fields. PHYSICAL REVIEW LETTERS 2009; 102:026806. [PMID: 19257306 DOI: 10.1103/physrevlett.102.026806] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2008] [Indexed: 05/27/2023]
Abstract
The misfit oxide, Bi2Ba1.3K0.6Co2.1O7.94, made of alternating rocksalt-structured [BiO/BaO] layers and hexagonal CoO2 layers, was studied by angle-resolved photoemission spectroscopy, revealing the electronic structure of a highly strained oxide interface. We found that low-energy states are confined within individual sides of the interface, but scattered by the incommensurate crystal field from the other side. Furthermore, the high strain on the rocksalt layer induces large charge transfer to the CoO2 layer, and a novel effect, the interfacial enhancement of electron-phonon interactions, is discovered.
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Affiliation(s)
- H W Ou
- Surface Physics Laboratory (National key laboratory) and Physics Department, Fudan University, Shanghai 200433, PR China
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25
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Yoshimatsu K, Yasuhara R, Kumigashira H, Oshima M. Origin of metallic states at the heterointerface between the band insulators LaAlO3 and SrTiO3. PHYSICAL REVIEW LETTERS 2008; 101:026802. [PMID: 18764211 DOI: 10.1103/physrevlett.101.026802] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2007] [Indexed: 05/26/2023]
Abstract
We have studied the electronic structure at the heterointerface between the band insulators LaAlO3 and SrTiO3 using in situ photoemission spectroscopy. Our experimental results clearly reveal the formation of a notched structure on the SrTiO3 side due to band bending at the metallic LaAlO3/TiO2-SrTiO3 interface. The structure, however, is absent at the insulating LaAlO3/SrO-SrTiO3 interface. The present results indicate that the metallic states originate not from the charge transfer through the interface on a short-range scale but from the accumulation of carriers on a long-range scale.
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Affiliation(s)
- K Yoshimatsu
- Department of Applied Chemistry, University of Tokyo, Tokyo 113-8656, Japan
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26
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González I, Okamoto S, Yunoki S, Moreo A, Dagotto E. Charge transfer in heterostructures of strongly correlated materials. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2008; 20:264002. [PMID: 21694336 DOI: 10.1088/0953-8984/20/26/264002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In this work, recent theoretical investigations by the authors in the area of oxide multilayers are briefly reviewed. The calculations were carried out using model Hamiltonians and a variety of non-perturbative techniques. Moreover, new results are also included here. They correspond to the generation of a metallic state by mixing insulators in a multilayer geometry, using the Hubbard and double-exchange models. For the latter, the resulting metallic state is also ferromagnetic. This illustrates how electron or hole doping via transfer of charge in multilayers can lead to the study of phase diagrams of transition metal oxides in the clean limit. Currently, these phase diagrams are much affected by the disordering standard chemical doping procedure, which introduces quenched disorder in the material.
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Affiliation(s)
- I González
- Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN 37996, USA. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
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27
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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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28
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Johnsson M, Lemmens P. Perovskites and thin films-crystallography and chemistry. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2008; 20:264001. [PMID: 21694335 DOI: 10.1088/0953-8984/20/26/264001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We discuss the crystallographic and chemical basis of the perovskite family (ABX(3)) of oxides that are used in different thin film applications. Starting with the original structure we extend our scope to several modifications. Basic parameters like the ionic radii, the tolerance factor, the occupation of the oxygen sublattice and their effect on the structural parameters will be mentioned together with examples of relationships between structural and physical properties in the bulk and at interfaces.
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Affiliation(s)
- Mats Johnsson
- Department of Inorganic Chemistry, Stockholm University, S-106 91 Stockholm, Sweden
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29
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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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30
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Smadici S, Abbamonte P, Bhattacharya A, Zhai X, Jiang B, Rusydi A, Eckstein JN, Bader SD, Zuo JM. Electronic reconstruction at SrMnO3-LaMnO3 superlattice interfaces. PHYSICAL REVIEW LETTERS 2007; 99:196404. [PMID: 18233095 DOI: 10.1103/physrevlett.99.196404] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2007] [Indexed: 05/25/2023]
Abstract
We use resonant soft-x-ray scattering (RSXS) to study the electronic reconstruction at the interface between the Mott insulator LaMnO3 and the band insulator SrMnO3. Superlattices of these two insulators were shown previously to have both ferromagnetism and metallic tendencies [Koida, Phys. Rev. B 66, 144418 (2002)10.1103/PhysRevB.66.144418]. By studying a judiciously chosen superlattice reflection, we show that the interface density of states exhibits a pronounced peak at the Fermi level, similar to that predicted in related titanate superlattices by Okamoto et al. [Phys. Rev. B 70, 241104(R) (2004)10.1103/PhysRevB.70.241104]. The intensity of this peak correlates with the conductivity and magnetization, suggesting it is the driver of metallic behavior. Our study demonstrates a general strategy for using RSXS to probe the electronic properties of heterostructure interfaces.
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Affiliation(s)
- Serban Smadici
- Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA
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31
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Willmott PR, Pauli SA, Herger R, Schlepütz CM, Martoccia D, Patterson BD, Delley B, Clarke R, Kumah D, Cionca C, Yacoby Y. Structural basis for the conducting interface between LaAlO3 and SrTiO3. PHYSICAL REVIEW LETTERS 2007; 99:155502. [PMID: 17995179 DOI: 10.1103/physrevlett.99.155502] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2007] [Indexed: 05/25/2023]
Abstract
The complete atomic structure of a five-monolayer film of LaAlO3 on SrTiO3 has been determined for the first time by surface x-ray diffraction in conjunction with the coherent Bragg rod analysis phase-retrieval method and further structural refinement. Cationic mixing at the interface results in dilatory distortions and the formation of metallic La(1-x)SrxTiO3. By invoking electrostatic potential minimization, the ratio of Ti{4+}/Ti{3+} across the interface was determined, from which the lattice dilation could be quantitatively explained using ionic radii considerations. The correctness of this model is supported by density functional theory calculations. Thus, the formation of a quasi-two-dimensional electron gas in this system is explained, based on structural considerations.
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Affiliation(s)
- P R Willmott
- Paul Scherrer Institut, CH-5232 Villigen, Switzerland.
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32
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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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33
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Brinkman A, Huijben M, van Zalk M, Huijben J, Zeitler U, Maan JC, van der Wiel WG, Rijnders G, Blank DHA, Hilgenkamp H. Magnetic effects at the interface between non-magnetic oxides. NATURE MATERIALS 2007; 6:493-6. [PMID: 17546035 DOI: 10.1038/nmat1931] [Citation(s) in RCA: 465] [Impact Index Per Article: 27.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2006] [Accepted: 05/02/2007] [Indexed: 05/15/2023]
Abstract
The electronic reconstruction at the interface between two insulating oxides can give rise to a highly conductive interface. Here we show how, in analogy to this remarkable interface-induced conductivity, magnetism can be induced at the interface between the otherwise non-magnetic insulating perovskites SrTiO3 and LaAlO3. A large negative magnetoresistance of the interface is found, together with a logarithmic temperature dependence of the sheet resistance. At low temperatures, the sheet resistance reveals magnetic hysteresis. Magnetic ordering is a key issue in solid-state science and its underlying mechanisms are still the subject of intense research. In particular, the interplay between localized magnetic moments and the spin of itinerant conduction electrons in a solid gives rise to intriguing many-body effects such as Ruderman-Kittel-Kasuya-Yosida interactions, the Kondo effect and carrier-induced ferromagnetism in diluted magnetic semiconductors. The conducting oxide interface now provides a versatile system to induce and manipulate magnetic moments in otherwise non-magnetic materials.
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Affiliation(s)
- A Brinkman
- Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands.
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