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Christensen DV, Steegemans TS, D Pomar T, Chen YZ, Smith A, Strocov VN, Kalisky B, Pryds N. Extreme magnetoresistance at high-mobility oxide heterointerfaces with dynamic defect tunability. Nat Commun 2024; 15:4249. [PMID: 38762504 PMCID: PMC11102559 DOI: 10.1038/s41467-024-48398-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Accepted: 04/30/2024] [Indexed: 05/20/2024] Open
Abstract
Magnetic field-induced changes in the electrical resistance of materials reveal insights into the fundamental properties governing their electronic and magnetic behavior. Various classes of magnetoresistance have been realized, including giant, colossal, and extraordinary magnetoresistance, each with distinct physical origins. In recent years, extreme magnetoresistance (XMR) has been observed in topological and non-topological materials displaying a non-saturating magnetoresistance reaching 103-108% in magnetic fields up to 60 T. XMR is often intimately linked to a gapless band structure with steep bands and charge compensation. Here, we show that a linear XMR of 80,000% at 15 T and 2 K emerges at the high-mobility interface between the large band-gap oxides γ-Al2O3 and SrTiO3. Despite the chemically and electronically very dissimilar environment, the temperature/field phase diagrams of γ-Al2O3/SrTiO3 bear a striking resemblance to XMR semimetals. By comparing magnetotransport, microscopic current imaging, and momentum-resolved band structures, we conclude that the XMR in γ-Al2O3/SrTiO3 is not strongly linked to the band structure, but arises from weak disorder enforcing a squeezed guiding center motion of electrons. We also present a dynamic XMR self-enhancement through an autonomous redistribution of quasi-mobile oxygen vacancies. Our findings shed new light on XMR and introduce tunability using dynamic defect engineering.
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Affiliation(s)
- D V Christensen
- Department of Energy Conversion and Storage, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark.
| | - T S Steegemans
- Department of Energy Conversion and Storage, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark
| | - T D Pomar
- Department of Energy Conversion and Storage, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark
| | - Y Z Chen
- Department of Energy Conversion and Storage, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - A Smith
- Department of Energy Conversion and Storage, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark
| | - V N Strocov
- Swiss Light Source, Paul Scherrer Institute, 5232, Villigen-PSI, Switzerland
| | - B Kalisky
- Department of Physics and Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 5290002, Israel
| | - N Pryds
- Department of Energy Conversion and Storage, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark
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2
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Düring PM, Rosenberger P, Baumgarten L, Alarab F, Lechermann F, Strocov VN, Müller M. Tunable 2D Electron- and 2D Hole States Observed at Fe/SrTiO 3 Interfaces. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024; 36:e2309217. [PMID: 38245856 DOI: 10.1002/adma.202309217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Revised: 10/27/2023] [Indexed: 01/22/2024]
Abstract
Oxide electronics provide the key concepts and materials for enhancing silicon-based semiconductor technologies with novel functionalities. However, a basic but key property of semiconductor devices still needs to be unveiled in its oxidic counterparts: the ability to set or even switch between two types of carriers-either negatively (n) charged electrons or positively (p) charged holes. Here, direct evidence for individually emerging n- or p-type 2D band dispersions in STO-based heterostructures is provided using resonant photoelectron spectroscopy. The key to tuning the carrier character is the oxidation state of an adjacent Fe-based interface layer: For Fe and FeO, hole bands emerge in the empty bandgap region of STO due to hybridization of Ti- and Fe- derived states across the interface, while for Fe3O4 overlayers, an 2D electron system is formed. Unexpected oxygen vacancy characteristics arise for the hole-type interfaces, which as of yet had been exclusively assigned to the emergence of 2DESs. In general, this finding opens up the possibility to straightforwardly switch the type of conductivity at STO interfaces by the oxidation state of a redox overlayer. This will extend the spectrum of phenomena in oxide electronics, including the realization of combined n/p-type all-oxide transistors or logic gates.
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Affiliation(s)
- Pia M Düring
- Fachbereich Physik, Universität Konstanz, 78457, Konstanz, Germany
| | - Paul Rosenberger
- Fachbereich Physik, Universität Konstanz, 78457, Konstanz, Germany
- Fakultät Physik, Technische Universität Dortmund, 44221, Dortmund, Germany
| | - Lutz Baumgarten
- Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI-6), 52425, Jülich, Germany
| | - Fatima Alarab
- Paul Scherrer Institute, Swiss Light Source, Villingen PSI, CH-5232, Switzerland
| | - Frank Lechermann
- Institut für Theoretische Physik III, Ruhr-Universität Bochum, 44780, Bochum, Germany
| | - Vladimir N Strocov
- Paul Scherrer Institute, Swiss Light Source, Villingen PSI, CH-5232, Switzerland
| | - Martina Müller
- Fachbereich Physik, Universität Konstanz, 78457, Konstanz, Germany
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3
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Yang Z, Wang L, Dhas JA, Engelhard MH, Bowden ME, Liu W, Zhu Z, Wang C, Chambers SA, Sushko PV, Du Y. Guided anisotropic oxygen transport in vacancy ordered oxides. Nat Commun 2023; 14:6068. [PMID: 37770428 PMCID: PMC10539514 DOI: 10.1038/s41467-023-40746-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Accepted: 08/07/2023] [Indexed: 09/30/2023] Open
Abstract
Anisotropic and efficient transport of ions under external stimuli governs the operation and failure mechanisms of energy-conversion systems and microelectronics devices. However, fundamental understanding of ion hopping processes is impeded by the lack of atomically precise materials and probes that allow for the monitoring and control at the appropriate time- and length- scales. In this work, using in-situ transmission electron microscopy, we directly show that oxygen ion migration in vacancy ordered, semiconducting SrFeO2.5 epitaxial thin films can be guided to proceed through two distinctly different diffusion pathways, each resulting in different polymorphs of SrFeO2.75 with different ground electronic properties before reaching a fully oxidized, metallic SrFeO3 phase. The diffusion steps and reaction intermediates are revealed by means of ab-initio calculations. The principles of controlling oxygen diffusion pathways and reaction intermediates demonstrated here may advance the rational design of structurally ordered oxides for tailored applications and provide insights for developing devices with multiple states of regulation.
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Affiliation(s)
- Zhenzhong Yang
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
- Key Laboratory of Polar Materials and Devices (MOE), Department of Electronics, East China Normal University, Shanghai, 200241, P. R. China
| | - Le Wang
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
| | - Jeffrey A Dhas
- School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, OR, 97331, USA
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
| | - Mark H Engelhard
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
| | - Mark E Bowden
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
| | - Wen Liu
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
- State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, 430074, China
| | - Zihua Zhu
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
| | - Chongmin Wang
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
| | - Scott A Chambers
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
| | - Peter V Sushko
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99354, USA.
| | - Yingge Du
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99354, USA.
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4
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Noh S, Choe D, Jin H, Yoo JW. Enhancement of the Rashba Effect in a Conducting SrTiO 3 Surface by MoO 3 Capping. ACS APPLIED MATERIALS & INTERFACES 2022; 14:50280-50287. [PMID: 36282511 DOI: 10.1021/acsami.2c11840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Systems having inherent structural asymmetry retain the Rashba-type spin-orbit interaction, which ties the spin and momentum of electrons in the band structure, leading to coupled spin and charge transport. One of the electrical manifestations of the Rashba spin-orbit interaction is nonreciprocal charge transport, which could be utilized for rectifying devices. Further tuning of the Rashba spin-orbit interaction allows additional functionalities in spin-orbitronic applications. In this work, we present our study of nonreciprocal charge transport in a conducting SrTiO3 (001) surface and its significant enhancement by a capping layer. The conductive strontium titanate SrTiO3 (STO) (001) surface was created through oxygen vacancies by Ar+ irradiation, and the nonreciprocal signal was probed by angle- and magnetic field-dependent second harmonic voltage measurement with an AC current. We observed robust directional transport in the Ar+-irradiated sample at low temperatures. The magnitude of the nonreciprocal signal is highly dependent on the irradiation time as it affects the depth of the conducting layer and the impact of the topmost conducting layer. Moreover, the nonreciprocal resistance was significantly enhanced by simply adding a MoO3 capping layer on the conductive STO surface. These results show a simple methodology for tuning and investigating the Rashba effect in a conductive STO surface, which could be adopted for various two-dimensional (2D) conducting layers for spin-orbitronic applications.
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Affiliation(s)
- Seunghyeon Noh
- Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan44919, Korea
| | - Daeseong Choe
- Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan44919, Korea
| | - Hosub Jin
- Department of Physics, Ulsan National Institute of Science and Technology, Ulsan44919, Korea
| | - Jung-Woo Yoo
- Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan44919, Korea
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5
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Chikina A, Christensen DV, Borisov V, Husanu MA, Chen Y, Wang X, Schmitt T, Radovic M, Nagaosa N, Mishchenko AS, Valentí R, Pryds N, Strocov VN. Band-Order Anomaly at the γ-Al 2O 3/SrTiO 3 Interface Drives the Electron-Mobility Boost. ACS NANO 2021; 15:4347-4356. [PMID: 33661601 DOI: 10.1021/acsnano.0c07609] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The rich functionalities of transition-metal oxides and their interfaces bear an enormous technological potential. Its realization in practical devices requires, however, a significant improvement of yet relatively low electron mobility in oxide materials. Recently, a mobility boost of about 2 orders of magnitude has been demonstrated at the spinel-perovskite γ-Al2O3/SrTiO3 interface compared to the paradigm perovskite-perovskite LaAlO3/SrTiO3 interface. We explore the fundamental physics behind this phenomenon from direct measurements of the momentum-resolved electronic structure of this interface using resonant soft-X-ray angle-resolved photoemission. We find an anomaly in orbital ordering of the mobile electrons in γ-Al2O3/SrTiO3 which depopulates electron states in the top SrTiO3 layer. This rearrangement of the mobile electron system pushes the electron density away from the interface, which reduces its overlap with the interfacial defects and weakens the electron-phonon interaction, both effects contributing to the mobility boost. A crystal-field analysis shows that the band order alters owing to the symmetry breaking between the spinel γ-Al2O3 and perovskite SrTiO3. Band-order engineering, exploiting the fundamental symmetry properties, emerges as another route to boost the performance of oxide devices.
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Affiliation(s)
- Alla Chikina
- Swiss Light Source, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
- Institute of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus, Denmark
| | - Dennis V Christensen
- Department of Energy Conversion and Storage, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Vladislav Borisov
- Institut für Theoretische Physik, Goethe-Universität Frankfurt am Main, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany
- Department of Physics and Astronomy, Uppsala University, Box 516, 5120 Uppsala, Sweden
| | - Marius-Adrian Husanu
- Swiss Light Source, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
- National Institute of Materials Physics, Atomistilor 405A, 077125 Magurele, Romania
| | - Yunzhong Chen
- Department of Energy Conversion and Storage, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Xiaoqiang Wang
- Swiss Light Source, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
| | - Thorsten Schmitt
- Swiss Light Source, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
| | - Milan Radovic
- Swiss Light Source, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
| | - Naoto Nagaosa
- RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Andrey S Mishchenko
- RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Roser Valentí
- Institut für Theoretische Physik, Goethe-Universität Frankfurt am Main, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany
| | - Nini Pryds
- Department of Energy Conversion and Storage, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Vladimir N Strocov
- Swiss Light Source, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
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6
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King PDC, Picozzi S, Egdell RG, Panaccione G. Angle, Spin, and Depth Resolved Photoelectron Spectroscopy on Quantum Materials. Chem Rev 2021; 121:2816-2856. [PMID: 33346644 DOI: 10.1021/acs.chemrev.0c00616] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The role of X-ray based electron spectroscopies in determining chemical, electronic, and magnetic properties of solids has been well-known for several decades. A powerful approach is angle-resolved photoelectron spectroscopy, whereby the kinetic energy and angle of photoelectrons emitted from a sample surface are measured. This provides a direct measurement of the electronic band structure of crystalline solids. Moreover, it yields powerful insights into the electronic interactions at play within a material and into the control of spin, charge, and orbital degrees of freedom, central pillars of future solid state science. With strong recent focus on research of lower-dimensional materials and modified electronic behavior at surfaces and interfaces, angle-resolved photoelectron spectroscopy has become a core technique in the study of quantum materials. In this review, we provide an introduction to the technique. Through examples from several topical materials systems, including topological insulators, transition metal dichalcogenides, and transition metal oxides, we highlight the types of information which can be obtained. We show how the combination of angle, spin, time, and depth-resolved experiments are able to reveal "hidden" spectral features, connected to semiconducting, metallic and magnetic properties of solids, as well as underlining the importance of dimensional effects in quantum materials.
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Affiliation(s)
- Phil D C King
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, United Kingdom
| | - Silvia Picozzi
- Consiglio Nazionale delle Ricerche, CNR-SPIN, Via dei Vestini 31, Chieti 66100, Italy
| | - Russell G Egdell
- Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom
| | - Giancarlo Panaccione
- Istituto Officina dei Materiali (IOM)-CNR, Laboratorio TASC, in Area Science Park, S.S.14, Km 163.5, I-34149 Trieste, Italy
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7
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Piyanzina II, Eyert V, Lysogorskiy YV, Tayurskii DA, Kopp T. Oxygen vacancies and hydrogen doping in LaAlO 3/SrTiO 3 heterostructures: electronic properties and impact on surface and interface reconstruction. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:295601. [PMID: 30970333 DOI: 10.1088/1361-648x/ab1831] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We investigate the effect of oxygen vacancies and hydrogen dopants at the surface and inside slabs of [Formula: see text], [Formula: see text], and [Formula: see text]/[Formula: see text] heterostructures on the electronic properties by means of electronic structure calculations as based on density functional theory. Depending on the concentration, the presence of these defects in a [Formula: see text] slab can suppress the surface conductivity. In contrast, in insulating [Formula: see text] slabs already very small concentrations of oxygen vacancies or hydrogen dopant atoms induce a finite occupation of the conduction band. Surface defects in insulating [Formula: see text]/[Formula: see text] heterostructure slabs with three [Formula: see text] overlayers lead to the emergence of interface conductivity. Calculated defect formation energies reveal strong preference of hydrogen dopant atoms for surface sites for all structures and concentrations considered. Strong decrease of the defect formation energy of hydrogen adatoms with increasing thickness of the [Formula: see text] overlayer and crossover from positive to negative values, taken together with the metallic conductivity induced by hydrogen adatoms, seamlessly explains the semiconductor-metal transition observed for these heterostructures as a function of the overlayer thickness. Moreover, we show that the potential drop and concomitant shift of (layer resolved) band edges is suppressed for the metallic configuration. Finally, magnetism with stable local moments, which form atomically thin magnetic layers at the interface, is generated by oxygen vacancies either at the surface or the interface, or by hydrogen atoms buried at the interface. In particular, oxygen vacancies in the [Formula: see text] interface layer cause drastic downshift of the 3d e g states of the Ti atoms neighboring the vacancies, giving rise to strongly localized magnetic moments, which add to the two-dimensional background magnetization.
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Affiliation(s)
- I I Piyanzina
- Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, 86135 Augsburg, Germany. Institute of Physics, Kazan Federal University, 420008 Kazan, Russia
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8
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Baeumer C, Heisig T, Arndt B, Skaja K, Borgatti F, Offi F, Motti F, Panaccione G, Waser R, Menzel S, Dittmann R. Spectroscopic elucidation of ionic motion processes in tunnel oxide-based memristive devices. Faraday Discuss 2019; 213:215-230. [PMID: 30364919 DOI: 10.1039/c8fd00108a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Resistive switching oxides are highly attractive candidates to emulate synaptic behaviour in artificial neural networks. Whilst the most widely employed systems exhibit filamentary resistive switching, interface-type switching systems based on a tunable tunnel barrier are of increasing interest, since their gradual SET and RESET processes provide an analogue-type of switching required to take over synaptic functionality. Interface-type switching devices often consist of bilayers of one highly mixed-conductive oxide layer and one highly insulating tunnel oxide layer. However, most tunnel oxides used for interface-type switching are also prone to form conducting filaments above a certain voltage bias threshold. We investigated two different tunnel oxide devices, namely, Pr1-xCaxMnO3 (PCMO) with yttria-stabilized ZrO2 (YSZ) tunnel barrier and substoichiometric TaOx with HfO2 tunnel barrier by interface-sensitive, hard X-ray photoelectron spectroscopy (HAXPES) in order to gain insights into the chemical changes during filamentary and interface-type switching. The measurements suggest an exchange of oxygen ions between the mixed conducting oxide layer and the tunnel barrier, that causes an electrostatic modulation of the effective height of the tunnel barrier, as the underlying switching mechanism for the interface-type switching. Moreover, we observe by in operando HAXPES analysis that this field-driven ionic motion across the whole area is sustained even if a filament is formed in the tunnel barrier and the device is transformed into a filamentary-type switching mode.
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Affiliation(s)
- Christoph Baeumer
- Peter Gruenberg Institute 7, Forschungszentrum Juelich GmbH, JARA-FIT, 52425 Juelich, Germany.
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9
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Baeumer C, Funck C, Locatelli A, Menteş TO, Genuzio F, Heisig T, Hensling F, Raab N, Schneider CM, Menzel S, Waser R, Dittmann R. In-Gap States and Band-Like Transport in Memristive Devices. NANO LETTERS 2019; 19:54-60. [PMID: 30241437 DOI: 10.1021/acs.nanolett.8b03023] [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
Point defects such as oxygen vacancies cause emergent phenomena such as resistive switching in transition-metal oxides, but their influence on the electron-transport properties is far from being understood. Here, we employ direct mapping of the electronic structure of a memristive device by spectromicroscopy. We find that oxygen vacancies result in in-gap states that we use as input for single-band transport simulations. Because the in-gap states are situated below the Fermi level, they do not contribute to the current directly but impact the shape of the conduction band. Accordingly, we can describe our devices with band-like transport and tunneling across the Schottky barrier at the interface.
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Affiliation(s)
- Christoph Baeumer
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Carsten Funck
- Institute for Electronic Materials, IWE2 , RWTH Aachen University , 52074 Aachen , Germany
| | - Andrea Locatelli
- Elettra - Sincrotrone Trieste S.C.p.A., S.S. 14 km - 163,5 in AREA Science Park , I-34149 Basovizza , Trieste , Italy
| | - Tevfik Onur Menteş
- Elettra - Sincrotrone Trieste S.C.p.A., S.S. 14 km - 163,5 in AREA Science Park , I-34149 Basovizza , Trieste , Italy
| | - Francesca Genuzio
- Elettra - Sincrotrone Trieste S.C.p.A., S.S. 14 km - 163,5 in AREA Science Park , I-34149 Basovizza , Trieste , Italy
| | - Thomas Heisig
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Felix Hensling
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Nicolas Raab
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Claus M Schneider
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Stephan Menzel
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Rainer Waser
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
- Institute for Electronic Materials, IWE2 , RWTH Aachen University , 52074 Aachen , Germany
| | - Regina Dittmann
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
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10
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Mathieu C, Gonzalez S, Lubin C, Copie O, Feyer V, Schneider CM, Barrett N. High-temperature 2D Fermi surface of SrTiO3
studied by energy-filtered PEEM. SURF INTERFACE ANAL 2018. [DOI: 10.1002/sia.6533] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Claire Mathieu
- SPEC, CEA, CNRS; Université Paris-Saclay, CEA Saclay; Gif-sur-Yvette Cedex France
| | - Sara Gonzalez
- SPEC, CEA, CNRS; Université Paris-Saclay, CEA Saclay; Gif-sur-Yvette Cedex France
- BaDElPh beamline; Elettra-Sincrotrone Trieste; S.S. 14 km 163.5 in AREA Science Park Basovizza I-34149 Trieste Italy
| | - Christophe Lubin
- SPEC, CEA, CNRS; Université Paris-Saclay, CEA Saclay; Gif-sur-Yvette Cedex France
| | - Olivier Copie
- Institut Jean Lamour; UMR 7198 CNRS/Université de Lorraine; Vandoeuvre-lès-Nancy France
| | - Vitaliy Feyer
- Peter Grünberg Institute (PGI-6); JARA-FIT, Research Center Jülich; Jülich Germany
- NanoESCA beamline; Elettra-Sincrotrone Trieste; S.S. 14 km 163.5 in AREA Science Park Basovizza I-34149 Trieste Italy
| | - Claus M. Schneider
- Peter Grünberg Institute (PGI-6); JARA-FIT, Research Center Jülich; Jülich Germany
| | - Nick Barrett
- SPEC, CEA, CNRS; Université Paris-Saclay, CEA Saclay; Gif-sur-Yvette Cedex France
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11
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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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12
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Rodenbücher C, Bihlmayer G, Speier W, Kubacki J, Wojtyniak M, Rogala M, Wrana D, Krok F, Szot K. Local surface conductivity of transition metal oxides mapped with true atomic resolution. NANOSCALE 2018; 10:11498-11505. [PMID: 29888770 DOI: 10.1039/c8nr02562b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The introduction of transition metal oxides for building nanodevices in information technology promises to overcome the scaling limits of conventional semiconductors and to reduce global power consumption significantly. However, oxide surfaces can exhibit heterogeneity on the nanoscale e.g. due to relaxation, rumpling, reconstruction, or chemical variations which demands for direct characterization of electronic transport phenomena down to the atomic level. Here we demonstrate that conductivity mapping is possible with true atomic resolution using the tip of a local conductivity atomic force microscope (LC-AFM) as the mobile nanoelectrode. The application to the prototypical transition metal oxide TiO2 self-doped by oxygen vacancies reveals the existence of highly confined current paths in the first stage of thermal reduction. Assisted by density functional theory (DFT) we propose that the presence of oxygen vacancies in the surface layer of such materials can introduce short range disturbances of the electronic structure with confinement of metallic states on the sub-nanometre scale. After prolonged reduction, the surfaces undergo reconstruction and the conductivity changes from spot-like to homogeneous as a result of surface transformation. The periodic arrangement of the reconstruction is clearly reflected in the conductivity maps as concluded from the simultaneous friction force and LC-AFM measurements. The second prototype metal oxide SrTiO3 also reveals a comparable transformation in surface conductivity from spot-like to homogeneous upon reduction showing the relevance of nanoscale inhomogeneities for the electronic transport properties and the utility of a high-resolution LC-AFM as a convenient tool to detect them.
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Affiliation(s)
- C Rodenbücher
- Forschungszentrum Jülich GmbH, Peter Grünberg Institute (PGI-1 & PGI-7), 52425 Jülich, Germany.
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13
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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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14
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Kormondy KJ, Gao L, Li X, Lu S, Posadas AB, Shen S, Tsoi M, McCartney MR, Smith DJ, Zhou J, Lev LL, Husanu MA, Strocov VN, Demkov AA. Large positive linear magnetoresistance in the two-dimensional t 2g electron gas at the EuO/SrTiO 3 interface. Sci Rep 2018; 8:7721. [PMID: 29769572 PMCID: PMC5955958 DOI: 10.1038/s41598-018-26017-z] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Accepted: 05/03/2018] [Indexed: 11/09/2022] Open
Abstract
The development of novel nano-oxide spintronic devices would benefit greatly from interfacing with emergent phenomena at oxide interfaces. In this paper, we integrate highly spin-split ferromagnetic semiconductor EuO onto perovskite SrTiO3 (001). A careful deposition of Eu metal by molecular beam epitaxy results in EuO growth via oxygen out-diffusion from SrTiO3. This in turn leaves behind a highly conductive interfacial layer through generation of oxygen vacancies. Below the Curie temperature of 70 K of EuO, this spin-polarized two-dimensional t 2g electron gas at the EuO/SrTiO3 interface displays very large positive linear magnetoresistance (MR). Soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) reveals the t 2g nature of the carriers. First principles calculations strongly suggest that Zeeman splitting, caused by proximity magnetism and oxygen vacancies in SrTiO3, is responsible for the MR. This system offers an as-yet-unexplored route to pursue proximity-induced effects in the oxide two-dimensional t 2g electron gas.
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Affiliation(s)
- Kristy J Kormondy
- Department of Physics, The University of Texas at Austin, Austin, Texas, 78712, USA
| | - Lingyuan Gao
- Department of Physics, The University of Texas at Austin, Austin, Texas, 78712, USA
| | - Xiang Li
- Materials Science and Engineering Program/Mechanical Engineering, University of Texas at Austin, Austin, Texas, 78712, USA
| | - Sirong Lu
- School of Engineering for Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287, USA
| | - Agham B Posadas
- Department of Physics, The University of Texas at Austin, Austin, Texas, 78712, USA
| | - Shida Shen
- Department of Physics, The University of Texas at Austin, Austin, Texas, 78712, USA
| | - Maxim Tsoi
- Department of Physics, The University of Texas at Austin, Austin, Texas, 78712, USA
| | - Martha R McCartney
- Department of Physics, Arizona State University, Tempe, Arizona, 85287, USA
| | - David J Smith
- Department of Physics, Arizona State University, Tempe, Arizona, 85287, USA
| | - Jianshi Zhou
- Materials Science and Engineering Program/Mechanical Engineering, University of Texas at Austin, Austin, Texas, 78712, USA
| | - Leonid L Lev
- Paul Scherrer Institute, Swiss Light Source, CH-5232, Villigen PSI, Switzerland.,National Research Centre "Kurchatov Institute", 1 Akademika Kurchatova pl., 123182, Moscow, Russia
| | - Marius-Adrian Husanu
- Paul Scherrer Institute, Swiss Light Source, CH-5232, Villigen PSI, Switzerland.,National Institute of Materials Physics, 405A Atomistilor Str., 077125, Magurele, Romania
| | - Vladimir N Strocov
- Paul Scherrer Institute, Swiss Light Source, CH-5232, Villigen PSI, Switzerland
| | - Alexander A Demkov
- Department of Physics, The University of Texas at Austin, Austin, Texas, 78712, USA.
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15
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Electrons and Polarons at Oxide Interfaces Explored by Soft-X-Ray ARPES. SPECTROSCOPY OF COMPLEX OXIDE INTERFACES 2018. [DOI: 10.1007/978-3-319-74989-1_6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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16
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Plumb NC, Radović M. Angle-resolved photoemission spectroscopy studies of metallic surface and interface states of oxide insulators. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:433005. [PMID: 28961143 DOI: 10.1088/1361-648x/aa833f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Over the last decade, conducting states embedded in insulating transition metal oxides (TMOs) have served as gateways to discovering and probing surprising phenomena that can emerge in complex oxides, while also opening opportunities for engineering advanced devices. These states are commonly realized at thin film interfaces, such as the well-known case of LaAlO3 (LAO) grown on SrTiO3 (STO). In recent years, the use of angle-resolved photoemission spectroscopy (ARPES) to investigate the k-space electronic structure of such materials led to the discovery that metallic states can also be formed on the bare surfaces of certain TMOs. In this topical review, we report on recent studies of low-dimensional metallic states confined at insulating oxide surfaces and interfaces as seen from the perspective of ARPES, which provides a direct view of the occupied band structure. While offering a fairly broad survey of progress in the field, we draw particular attention to STO, whose surface is so far the best-studied, and whose electronic structure is probably of the most immediate interest, given the ubiquitous use of STO substrates as the basis for conducting oxide interfaces. The ARPES studies provide crucial insights into the electronic band structure, orbital character, dimensionality/confinement, spin structure, and collective excitations in STO surfaces and related oxide surface/interface systems. The obtained knowledge increases our understanding of these complex materials and gives new perspectives on how to manipulate their properties.
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Affiliation(s)
- Nicholas C Plumb
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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17
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Eom K, Choi E, Choi M, Han S, Zhou H, Lee J. Oxygen Vacancy Linear Clustering in a Perovskite Oxide. J Phys Chem Lett 2017; 8:3500-3505. [PMID: 28707469 DOI: 10.1021/acs.jpclett.7b01348] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Oxygen vacancies have been implicitly assumed isolated ones, and understanding oxide materials possibly containing oxygen vacancies remains elusive within the scheme of the isolated vacancies, although the oxygen vacancies have been playing a decisive role in oxide materials. Here, we report the presence of oxygen vacancy linear clusters and their orientation along a specific crystallographic direction in SrTiO3, a representative of a perovskite oxide. The presence of the linear clusters and associated electron localization was revealed by an electronic structure represented in the increase in the Ti2+ valence state or corresponding Ti 3d2 electronic configuration along with divacancy cluster model analysis and transport measurement. The orientation of the linear clusters along the [001] direction in perovskite SrTiO3 was verified by further X-ray diffuse scattering analysis. Because SrTiO3 is an archetypical perovskite oxide, the vacancy linear clustering with the specific aligned direction and electron localization can be extended to a wide variety of the perovskite oxides.
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Affiliation(s)
- Kitae Eom
- School of Advanced Materials Science and Engineering, Sungkyunkwan University , Suwon 16419, Korea
| | - Euiyoung Choi
- School of Advanced Materials Science and Engineering, Sungkyunkwan University , Suwon 16419, Korea
| | - Minsu Choi
- School of Advanced Materials Science and Engineering, Sungkyunkwan University , Suwon 16419, Korea
| | - Seungwu Han
- Department of Materials Science and Engineering, Seoul National University , Seoul 08826, Korea
| | - Hua Zhou
- Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States
| | - Jaichan Lee
- School of Advanced Materials Science and Engineering, Sungkyunkwan University , Suwon 16419, Korea
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18
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Vaz DC, Lesne E, Sander A, Naganuma H, Jacquet E, Santamaria J, Barthélémy A, Bibes M. Tuning Up or Down the Critical Thickness in LaAlO 3 /SrTiO 3 through In Situ Deposition of Metal Overlayers. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2017; 29:1700486. [PMID: 28505388 DOI: 10.1002/adma.201700486] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 03/28/2017] [Indexed: 06/07/2023]
Abstract
The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 and SrTiO3 has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LaAlO3 thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. In this paper, the chemical, electronic, and transport properties of LaAlO3 /SrTiO3 samples capped with different metals grown in a system combining pulsed laser deposition, sputtering, and in situ X-ray photoemission spectroscopy are investigated. The results show that for metals with low work function a q2DES forms at 1-2 uc of LaAlO3 and is accompanied by a partial oxidation of the metal, a phenomenon that affects the q2DES properties and triggers the formation of defects. In contrast, for noble metals, the critical thickness is increased above 4 uc. The results are discussed in terms of a hybrid mechanism that incorporates electrostatic and chemical effects.
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Affiliation(s)
- Diogo Castro Vaz
- Unité Mixte de Physique UMR 137 CNRS/Thales, Université Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - Edouard Lesne
- Unité Mixte de Physique UMR 137 CNRS/Thales, Université Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - Anke Sander
- Unité Mixte de Physique UMR 137 CNRS/Thales, Université Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - Hiroshi Naganuma
- Unité Mixte de Physique UMR 137 CNRS/Thales, Université Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
- Department of Applied Physics, Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan
| | - Eric Jacquet
- Unité Mixte de Physique UMR 137 CNRS/Thales, Université Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - Jacobo Santamaria
- Unité Mixte de Physique UMR 137 CNRS/Thales, Université Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
- Instituto de Magnetismo Aplicado, Universidad Complutense de Madrid, 28040, Madrid, Spain
| | - Agnès Barthélémy
- Unité Mixte de Physique UMR 137 CNRS/Thales, Université Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - Manuel Bibes
- Unité Mixte de Physique UMR 137 CNRS/Thales, Université Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
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