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Ning Z, Qian J, Liu Y, Chen F, Zhang M, Deng L, Yuan X, Ge Q, Jin H, Zhang G, Peng W, Qiao S, Mu G, Chen Y, Li W. Coexistence of Ferromagnetism and Superconductivity at KTaO 3 Heterointerfaces. NANO LETTERS 2024; 24:7134-7141. [PMID: 38828962 DOI: 10.1021/acs.nanolett.4c02500] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2024]
Abstract
The coexistence of superconductivity and ferromagnetism is a long-standing issue in superconductivity due to the antagonistic nature of these two ordered states. Experimentally identifying and characterizing novel heterointerface superconductors that coexist with magnetism presents significant challenges. Here, we report the observation of two-dimensional long-range ferromagnetic order in a KTaO3 heterointerface superconductor, showing the coexistence of superconductivity and ferromagnetism. Remarkably, our direct current superconducting quantum interference device measurements reveal an in-plane magnetization hysteresis loop persisting above room temperature. Moreover, first-principles calculations and X-ray magnetic circular dichroism measurements provide decisive insights into the origin of the observed robust ferromagnetism, attributing it to oxygen vacancies that localize electrons in nearby Ta 5d states. Our findings suggest KTaO3 heterointerfaces as time-reversal symmetry breaking superconductors, injecting fresh momentum into the exploration of the intricate interplay between superconductivity and magnetism enhanced by the strong spin-orbit coupling inherent to the heavy Ta in 5d orbitals.
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Affiliation(s)
- Zhongfeng Ning
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Jiahui Qian
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Yixin Liu
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Fan Chen
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Mingzhu Zhang
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Liwei Deng
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xinli Yuan
- Thermo Fisher Scientific China, Shanghai 201203, China
| | - Qingqin Ge
- Thermo Fisher Scientific China, Shanghai 201203, China
| | - Hua Jin
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Guanqun Zhang
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Wei Peng
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Shan Qiao
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Gang Mu
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yan Chen
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Wei Li
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
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Tuvia G, Frenkel Y, Rout PK, Silber I, Kalisky B, Dagan Y. Ferroelectric Exchange Bias Affects Interfacial Electronic States. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e2000216. [PMID: 32510654 DOI: 10.1002/adma.202000216] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Revised: 04/20/2020] [Indexed: 06/11/2023]
Abstract
In polar oxide interfaces phenomena such as superconductivity, magnetism, 1D conductivity, and quantum Hall states can emerge at the polar discontinuity. Combining controllable ferroelectricity at such interfaces can affect the superconducting properties and sheds light on the mutual effects between the polar oxide and the ferroelectric oxide. Here, the interface between the polar oxide LaAlO3 and the ferroelectric Ca-doped SrTiO3 is studied by means of electrical transport combined with local imaging of the current flow with the use of scanning a superconducting quantum interference device (SQUID). Anomalous behavior of the interface resistivity is observed at low temperatures. The scanning SQUID maps of the current flow suggest that this behavior originates from an intrinsic bias induced by the polar LaAlO3 layer. Such intrinsic bias combined with ferroelectricity can constrain the possible structural domain tiling near the interface. The use of this intrinsic bias is recommended as a method of controlling and tuning the initial state of ferroelectric materials by the design of the polar structure. The hysteretic dependence of the normal and the superconducting state properties on gate voltage can be utilized in multifaceted controllable memory devices.
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Affiliation(s)
- Gal Tuvia
- Raymond and Beverly Sackler School of Physics, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Yiftach Frenkel
- Department of Physics and Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 5290002, Israel
| | - Prasanna K Rout
- Raymond and Beverly Sackler School of Physics, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Itai Silber
- Raymond and Beverly Sackler School of Physics, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Beena Kalisky
- Department of Physics and Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 5290002, Israel
| | - Yoram Dagan
- Raymond and Beverly Sackler School of Physics, Tel Aviv University, Tel Aviv, 6997801, Israel
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3
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Chi X, Wang H, Guo R, Whitcher TJ, Yu X, Yang P, Yan X, Breese MBH, Loh KP, Chen J, Rusydi A. Unusual Hole and Electron Midgap States and Orbital Reconstructions Induced Huge Ferroelectric Tunneling Electroresistance in BaTiO 3/SrTiO 3. NANO LETTERS 2020; 20:1101-1109. [PMID: 31944125 DOI: 10.1021/acs.nanolett.9b04390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Oxide heterostructures have attracted a lot of interest because of their rich exotic phenomena and potential applications. Recently, a greatly enhanced tunneling electroresistance (TER) of ferroelectric tunnel junctions (FTJs) has been realized in such heterostructures. However, our understanding on the electronic structure of resistance response with polarization reversal and the origin of huge TER is still lacking. Here, we report on electronic structures, particularly at the interface and surface, and the control of the spontaneous polarization of BaTiO3 films by changing the termination of a SrTiO3 substrate. Interestingly, unusual electron and hole midgap states are concurrently formed and accompanied by orbital reconstructions, which determine the ferroelectric polarization orientation in the BaTiO3/SrTiO3. Such unusual midgap states, which yield a strong electronic screening effect, reduce the ferroelectric barrier width and height, and pin the ferroelectric polarization, lead to a dramatic enhancement of the TER effect. The midgap states are also observed in BaTiO3 films on electron-doped Nb/SrTiO3 revealing its universality. Our result provides new insight into the origin of the huge TER effect and opens a new route for designing ferroelectric tunnel junction-based devices with huge TER through interface engineering.
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Affiliation(s)
- Xiao Chi
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
- Department of Chemistry , National University of Singapore , 3 Science Drive 3, 117543 , Singapore
- Center for Advanced 2D Materials and Graphene Research Centre , 2 Science Drive 2, 117526 , Singapore
| | - Han Wang
- Department of Materials Science and Engineering , National University of Singapore , 117575 , Singapore
| | - Rui Guo
- Department of Materials Science and Engineering , National University of Singapore , 117575 , Singapore
| | - Thomas J Whitcher
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
- Center for Advanced 2D Materials and Graphene Research Centre , 2 Science Drive 2, 117526 , Singapore
| | - Xiaojiang Yu
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
| | - Ping Yang
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
| | - Xiaobing Yan
- Department of Materials Science and Engineering , National University of Singapore , 117575 , Singapore
| | - Mark B H Breese
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
- Department of Physics , National University of Singapore , 2 Science Drive 3, 117542 , Singapore
| | - Kian Ping Loh
- Department of Chemistry , National University of Singapore , 3 Science Drive 3, 117543 , Singapore
- Center for Advanced 2D Materials and Graphene Research Centre , 2 Science Drive 2, 117526 , Singapore
- Solar Energy Research Institute of Singapore (SERIS) , 7 Engineering Drive 1, 117574 , Singapore
| | - Jingsheng Chen
- Department of Chemistry , National University of Singapore , 3 Science Drive 3, 117543 , Singapore
| | - Andrivo Rusydi
- Singapore Synchrotron Light Source , National University of Singapore , 5 Research Link, 117603 , Singapore
- Department of Physics , National University of Singapore , 2 Science Drive 3, 117542 , Singapore
- Center for Advanced 2D Materials and Graphene Research Centre , 2 Science Drive 2, 117526 , Singapore
- Solar Energy Research Institute of Singapore (SERIS) , 7 Engineering Drive 1, 117574 , Singapore
- NUSSNI-NanoCore , National University of Singapore , 117576 , Singapore
- Graduate School for Integrative Sciences and Engineering (NGS) , National University of Singapore , 28 Medical Drive, 117456 , Singapore
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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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5
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Zhang Y, Xie L, Kim J, Stern A, Wang H, Zhang K, Yan X, Li L, Liu H, Zhao G, Chi H, Gadre C, Lin Q, Zhou Y, Uher C, Chen T, Chu YH, Xia J, Wu R, Pan X. Discovery of a magnetic conductive interface in PbZr 0.2Ti 0.8O 3 /SrTiO 3 heterostructures. Nat Commun 2018; 9:685. [PMID: 29449561 PMCID: PMC5814552 DOI: 10.1038/s41467-018-02914-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Accepted: 01/06/2018] [Indexed: 11/09/2022] Open
Abstract
Emergent physical properties often arise at interfaces of complex oxide heterostructures due to the interplay between various degrees of freedom, especially those with polar discontinuities. It is desirable to explore if these structures may generate pure and controllable spin currents, which are needed to attain unmatched performance and energy efficiency in the next-generation spintronic devices. Here we report the emergence of a spin-polarized two-dimensional electron gas (SP-2DEG) at the interface of two insulators, SrTiO3 and PbZr0.2Ti0.8O3. This SP-2DEG is strongly localized at the interfacial Ti atoms, due to the interplay between Coulomb interaction and band bending, and can be tuned by the ferroelectric polarization. Our findings open a door for engineering ferroelectric/insulator interfaces to create tunable ferroic orders for magnetoelectric device applications and provide opportunities for designing multiferroic materials in heterostructures. Two-dimensional electron gases that form in some complex oxide heterostructures may have useful functional behavior due to the interaction of the parent materials. Here the authors show that PZT/STO interfaces can host a spin-polarized electron gas, even though the bulk materials are nonmagnetic.
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Affiliation(s)
- Yi Zhang
- Department of Chemical Engineering and Materials Science, University of California, Irvine, CA, 92697, USA
| | - Lin Xie
- National Laboratory of Solid State Microstructures and College of Engineering and Applied Sciences, Nanjing University, Nanjing, Jiangsu, 210093, China
| | - Jeongwoo Kim
- Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA
| | - Alex Stern
- Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA
| | - Hui Wang
- Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA
| | - Kui Zhang
- Department of Chemical Engineering and Materials Science, University of California, Irvine, CA, 92697, USA
| | - Xingxu Yan
- Department of Chemical Engineering and Materials Science, University of California, Irvine, CA, 92697, USA
| | - Linze Li
- Department of Chemical Engineering and Materials Science, University of California, Irvine, CA, 92697, USA
| | - Henry Liu
- Department of Materials Science and Engineering, National Chiao Tung University, HsinChu, 30010, Taiwan
| | - Gejian Zhao
- Department of Physics, Arizona State University, Tempe, Arizona, 85287, USA
| | - Hang Chi
- Department of Physics, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Chaitanya Gadre
- Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA
| | - Qiyin Lin
- Irvine Materials Research Institute, University of California, Irvine, CA, 92697, USA
| | - Yichun Zhou
- School of Materials Science and Engineering, Xiangtan University, Xiangtan, 411105, Hunan, China
| | - Ctirad Uher
- Department of Physics, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Tingyong Chen
- Department of Physics, Arizona State University, Tempe, Arizona, 85287, USA
| | - Ying-Hao Chu
- Department of Materials Science and Engineering, National Chiao Tung University, HsinChu, 30010, Taiwan
| | - Jing Xia
- Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA
| | - Ruqian Wu
- Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA
| | - Xiaoqing Pan
- Department of Chemical Engineering and Materials Science, University of California, Irvine, CA, 92697, USA. .,Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA.
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6
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Pai YY, Tylan-Tyler A, Irvin P, Levy J. Physics of SrTiO 3-based heterostructures and nanostructures: a review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:036503. [PMID: 29424362 DOI: 10.1088/1361-6633/aa892d] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
This review provides a summary of the rich physics expressed within SrTiO3-based heterostructures and nanostructures. The intended audience is researchers who are working in the field of oxides, but also those with different backgrounds (e.g., semiconductor nanostructures). After reviewing the relevant properties of SrTiO3 itself, we will then discuss the basics of SrTiO3-based heterostructures, how they can be grown, and how devices are typically fabricated. Next, we will cover the physics of these heterostructures, including their phase diagram and coupling between the various degrees of freedom. Finally, we will review the rich landscape of quantum transport phenomena, as well as the devices that elicit them.
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Affiliation(s)
- Yun-Yi Pai
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, United States of America. Pittsburgh Quantum Institute, Pittsburgh, PA 15260, United States of America
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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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8
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Tsai MS, Li CS, Guo ST, Song MY, Singh AK, Lee WL, Chu MW. Off-Stoichiometry Driven Carrier Density Variation at the Interface of LaAlO 3/SrTiO 3. Sci Rep 2017; 7:1770. [PMID: 28496105 PMCID: PMC5431992 DOI: 10.1038/s41598-017-02039-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 04/05/2017] [Indexed: 11/28/2022] Open
Abstract
The interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted enormous interests due to its rich physical phenomena, such as metallic nature, magnetism and superconductivity. In this work, we report our experimental investigations on the influence of the LAO stoichiometry to the metallic interface. Taking advantage of the oxide molecular beam epitaxy (MBE) technique, a series of high quality LAO films with different nominal La/Al ratios and LAO thicknesses were grown on the TiO2-terminated STO substrates, where systematic variations of the LAO lattice constant and transport property were observed. In particular, the sheet density can be largely reduced by nearly an order of magnitude with merely about 20% increase in the nominal La/Al ratio. Our finding provides an effective method on tuning the electron density of the two-dimensional electron liquid (2DEL) at the LAO/STO interface.
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Affiliation(s)
- Ming-Shiu Tsai
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan
| | - Chi-Sheng Li
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan
| | - Shih-Ting Guo
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan
| | - Ming-Yuan Song
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan
| | - Akhilesh Kr Singh
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan.
| | - Wei-Li Lee
- Institute of Physics, Academia Sinica, Nankang, Taipei, 11529, Taiwan.
| | - M-W Chu
- Center for Condensed Matter Sciences, National Taiwan University, Taipei, 10617, Taiwan
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9
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Wang F, Ren Z, Tian H, Yang SA, Xie Y, Lu Y, Jiang J, Han G, Yang K. Interfacial Multiferroics of TiO 2/PbTiO 3 Heterostructure Driven by Ferroelectric Polarization Discontinuity. ACS APPLIED MATERIALS & INTERFACES 2017; 9:1899-1906. [PMID: 27990804 DOI: 10.1021/acsami.6b13183] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Novel phenomena appear when two different oxide materials are combined together to form an interface. For example, at the interface of LaAlO3/SrTiO3, two-dimensional conductive states form to avoid the polar discontinuity, and magnetic properties are found at such an interface. In this work, we propose a new type of interface between two nonmagnetic and nonpolar oxides that could host a magnetic state, where it is the ferroelectric polarization discontinuity instead of the polar discontinuity that leads to the charge transfer, forming the interfacial magnetic state. As a concrete example, we investigate by first-principles calculations the heterostructures made of ferroelectric perovskite oxide PbTiO3 and nonferroelectric polarized oxide TiO2. We show that charge is transferred to the interfacial layer forming an interfacial ferromagnetic ordering that may persist up to room temperature. Especially, the strong coupling between bulk ferroelectric polarization and interface ferromagnetism represents a new type of magnetoelectric effect, which provides an ideal platform for exploring the intriguing interfacial multiferroics. The findings here are important not only for fundamental science but also for promising applications in nanoscale electronics and spintronics.
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Affiliation(s)
| | | | | | - Shengyuan A Yang
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design , Singapore 487372, Singapore
| | | | | | | | | | - Kesong Yang
- Department of NanoEngineering, University of California , San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
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10
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Cortie DL, Buck T, Dehn MH, Karner VL, Kiefl RF, Levy CDP, McFadden RML, Morris GD, McKenzie I, Pearson MR, Wang XL, MacFarlane WA. β-NMR Investigation of the Depth-Dependent Magnetic Properties of an Antiferromagnetic Surface. PHYSICAL REVIEW LETTERS 2016; 116:106103. [PMID: 27015494 DOI: 10.1103/physrevlett.116.106103] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2015] [Indexed: 06/05/2023]
Abstract
By measuring the prototypical antiferromagnet α-Fe_{2}O_{3}, we show that it is possible to determine the static spin orientation and dynamic spin correlations within nanometers from an antiferromagnetic surface using the nuclear spin polarization of implanted ^{8}Li^{+} ions detected with β-NMR. Remarkably, the first-order Morin spin reorientation in single crystal α-Fe_{2}O_{3} occurs at the same temperature at all depths between 1 and 100 nm from the (110) surface; however, the implanted nuclear spin experiences an increased 1/T_{1} relaxation rate at shallow depths revealing soft-surface magnons. The surface-localized dynamics decay towards the bulk with a characteristic length of ε=11±1 nm, closely matching the finite-size thresholds of hematite nanostructures.
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Affiliation(s)
- D L Cortie
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Chemistry Department, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - T Buck
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - M H Dehn
- Physik-Department, Technische Universität München, 85748 Garching bei München, Germany
| | - V L Karner
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - R F Kiefl
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada
| | - C D P Levy
- TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada
| | - R M L McFadden
- Chemistry Department, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - G D Morris
- TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada
| | - I McKenzie
- TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada
| | - M R Pearson
- TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada
| | - X L Wang
- Institute for Superconducting and Electronic Materials, University of Wollongong, NSW 2500, Australia
| | - W A MacFarlane
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Chemistry Department, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
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11
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Rotella H, Pautrat A, Copie O, Boullay P, David A, Mercey B, Morales M, Prellier W. Kondo effect goes anisotropic in vanadate oxide superlattices. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:435601. [PMID: 26444931 DOI: 10.1088/0953-8984/27/43/435601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We study the transport properties in SrVO3/LaVO3 (SVO/LVO) superlattices deposited on SrTiO3 (STO) substrates. We show that the electronic conduction occurs in the metallic LVO layers with a galvanomagnetism typical of a 2D Fermi surface. In addition, a Kondo-like component appears in both the thermal variation of resistivity and the magnetoresistance. Surprisingly, in this system where the STO interface does not contribute to the measured conduction, the Kondo correction is strongly anisotropic. We show that the growth temperature allows a direct control of this contribution. Finally, the key role of vanadium mixed valency stabilized by oxygen vacancies is enlightened.
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Affiliation(s)
- H Rotella
- Laboratoire CRISMAT, CNRS UMR 6508, ENSICAEN et Université de Caen, 6 Bd Maréchal Juin, 14050 Caen Cedex 4, France
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12
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Lee S. Sensitive detection of NMR for thin films. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2015; 71:1-10. [PMID: 26549846 DOI: 10.1016/j.ssnmr.2015.10.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Revised: 10/14/2015] [Accepted: 10/27/2015] [Indexed: 06/05/2023]
Abstract
NMR can provide valuable information about thin films, but its relatively low sensitivity allows data acquisition only from bulk samples. The sensitivity problem is circumvented by detection schemes with higher sensitivity and/or enhanced polarization. In most of these ingenious techniques, electrons play a central role through hyperfine interactions with the nuclei of interest or the conversion of the spin orientation to an electric charge. The state of the art in NMR is the control of a single nuclear spin state, the complete form of which is one of the ultimate goals of nanotechnology.
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Affiliation(s)
- Soonchil Lee
- Department of Physics, KAIST, 291 Daehakro, Yusongku 305-701, South Korea.
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13
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Nazir S, Cheng J, Behtash M, Luo J, Yang K. Interface Energetics and Charge Carrier Density Amplification by Sn-Doping in LaAlO3/SrTiO3 Heterostructure. ACS APPLIED MATERIALS & INTERFACES 2015; 7:14294-14302. [PMID: 26062403 DOI: 10.1021/acsami.5b02770] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Tailoring the two-dimensional electron gas (2DEG) at the n-type (TiO2)(0)/(LaO)(+1) interface between the polar LaAlO3 (LAO) and nonpolar SrTiO3 (STO) insulators can potentially provide desired functionalities for next-generation low-dimensional nanoelectronic devices. Here, we propose a new approach to tune the electronic and magnetic properties in the n-type LAO/STO heterostructure (HS) system via electron doping. In this work, we modeled four types of layer doped LAO/STO HS systems with Sn dopants at different cation sites and studied their electronic structures and interface energetics by using first-principles electronic structure calculations. We identified the thermodynamic stability conditions for each of the four proposed doped configurations with respect to the undoped LAO/STO interface. We further found that the Sn-doped LAO/STO HS system with Sn at Al site (Sn@Al) is energetically most favorable with respect to decohesion, thereby strengthening the interface, while the doped HS system with Sn at La site (Sn@La) exhibits the lowest interfacial cohesion. Moreover, our results indicate that all the Sn-doped LAO/STO HS systems exhibit the n-type conductivity with the typical 2DEG characteristics except the Sn@La doped HS system, which shows p-type conductivity. In the Sn@Al doped HS model, the Sn dopant exists as a Sn(4+) ion and introduces one additional electron into the HS system, leading to a higher charge carrier density and larger magnetic moment than that of all the other doped HS systems. An enhanced charge confinement of the 2DEG along the c-axis is also found in the Sn@Al doped HS system. We hence suggest that Sn@Al doping can be an effective way to enhance the electrical conduction and magnetic moment of the 2DEG in LAO/STO HS systems in an energetically favorable manner.
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Affiliation(s)
- Safdar Nazir
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Jianli Cheng
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Maziar Behtash
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Jian Luo
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Kesong Yang
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
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14
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Gor'kov LP. Antiferromagnetism of two-dimensional electronic gas on light-irradiated SrTiO3 and at LaAlO3/SrTiO3 interfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:252001. [PMID: 26020368 DOI: 10.1088/0953-8984/27/25/252001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
To gain an insight into the origin of tunable two-dimensional (2D) electronic liquid at the interfaces of transition-metal oxides, we address properties of a conducting layer on the light-irradiated surfaces of SrTiO3; the energy spectrum of the latter is known and consists of the titanium dxz/dyz and dxy bands. Recently, Santander-Syro et al (2014 Nature Mater. 13 1085) revealed that the dxy bands actually comprise two chiral branches with the Kramers degeneracy at the zone center lifted in the absence of a magnetic moment. We suggest that interacting electrons on the irradiated SrTiO3 go over into a magnetic phase as the result of one of the instabilities of the 2D Fermi liquid with exchange interactions, and point out the concrete antiferromagnetic order parameter. Large energy scales of the order of Fermi energy ∼0.1 eV inherent in this mechanism warrant stability of the magnetic ground state against ever-present effects of disorder. Arguments are given that electrons at the irradiated SrTiO3 surface and at the LaAlO3/SrTiO3 interfaces undergo a kind of first-order transformation into one and the same phase of the 2D electronic Fermi liquid with reduced magnetic symmetry.
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Affiliation(s)
- L P Gor'kov
- NHMFL, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA. L.D. Landau Institute for Theoretical Physics of the RAS, Chernogolovka 142432, Russia
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15
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MacFarlane WA. Implanted-ion βNMR: A new probe for nanoscience. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2015; 68-69:1-12. [PMID: 25863576 DOI: 10.1016/j.ssnmr.2015.02.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Revised: 02/09/2015] [Accepted: 02/11/2015] [Indexed: 06/04/2023]
Abstract
NMR detected by radioactive beta decay, β-NMR, is undergoing a renaissance largely due to the availability of high intensity low energy beams of the most common probe ion, Li+8, and dedicated facilities for materials research. The radioactive detection scheme, combined with the low energy ion beam, enable depth resolved NMR measurements in crystals, thin films and multilayers on depth scales of 2-200 nm. After a brief historical introduction, technical aspects of implanted-ion β-NMR are presented, followed by a review of recent applications to a wide range of solids.
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Affiliation(s)
- W A MacFarlane
- Chemistry Department, University of British Columbia, 2036 Main Mall, Vancouver, Canada V6T 1Z1.
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16
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Garcia Ruiz RF, Bissell M, Gottberg A, Stachura M, Hemmingsen L, Neyens G, Severijns N. Perspectives for the VITO beam line at ISOLDE, CERN. EPJ WEB OF CONFERENCES 2015. [DOI: 10.1051/epjconf/20159307004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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17
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Nazir S, Bernal C, Yang K. Modulated two-dimensional charge-carrier density in LaTiO3-layer-doped LaAlO3/SrTiO3 heterostructure. ACS APPLIED MATERIALS & INTERFACES 2015; 7:5305-5311. [PMID: 25688656 DOI: 10.1021/am508662q] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The highly mobile two-dimensional electron gas (2DEG) formed at the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) is a matter of great interest because of its potential applications in nanoscale solid-state devices. To realize practical implementation of the 2DEG in device design, desired physical properties such as tuned charge carrier density and mobility are necessary. In this regard, polar perovskite-based transition metal oxides can act as doping layers at the interface and are expected to tune the electronic properties of 2DEG of STO-based HS systems dramatically. Herein, we investigated the doping effects of LaTiO3(LTO) layers on the electronic properties of 2DEG at n-type (LaO)(+1)/(TiO2)(0) interface in the LAO/STO HS using spin-polarized density functional theory calculations. Our results indicate an enhancement of orbital occupation near the Fermi energy, which increases with respect to the number of LTO unit cells, resulting in a higher charge carrier density of 2DEG than that of undoped system. The enhanced charge carrier density is attributed to an extra electron introduced by the Ti 3d(1) orbitals from the LTO dopant unit cells. This conclusion is consistent with the recent experimental findings (Appl. Phys. Lett. 2013, 102, 091601). Detailed charge density and partial density of states analysis suggests that the 2DEG in the LTO-doped HS systems primarily comes from partially occupied dyz and dxz orbitals.
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Affiliation(s)
- Safdar Nazir
- Department of NanoEngineering, University of California, San Diego , 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
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18
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McKenzie I, Daley CR, Kiefl RF, Levy CDP, MacFarlane WA, Morris GD, Pearson MR, Wang D, Forrest JA. Enhanced high-frequency molecular dynamics in the near-surface region of polystyrene thin films observed with β-NMR. SOFT MATTER 2015; 11:1755-1761. [PMID: 25605007 DOI: 10.1039/c4sm02245a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
β-detected nuclear spin relaxation of (8)Li(+) has been used to probe the depth dependence of molecular dynamics in high- and low-molecular-weight deuterated polystyrene. The average nuclear spin-lattice relaxation rate, 1/T(avg)(1), is a measure of the spectral density of the polymer motion at the Larmor frequency (41 MHz at 6.55 T). In both samples, 1/T(avg)(1) is depth independent below ∼200 K but above this temperature it decreases approximately exponentially with distance from the free surface, returning to bulk behavior for depths greater than ∼10 nm. This is direct evidence for a region near the free surface with enhanced molecular dynamics compared with the bulk. The effective thickness of the surface region increases with increasing temperature and is finite even above the glass transition. These results present challenges for the current understanding of dynamics near the surface of polymer glasses.
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19
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Gao D, Zhang Z, Li Y, Xia B, Shi S, Xue D. Abnormal room temperature ferromagnetism in CuO–ZnO heterostructures: interface related or not? Chem Commun (Camb) 2015; 51:1151-3. [PMID: 25470613 DOI: 10.1039/c4cc08485c] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report the new functionality of room temperature ferromagnetism in CuO–ZnO heterostructures.
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Affiliation(s)
- Daqiang Gao
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education
- Key Laboratory of Special Function Materials and Structure Design
- Ministry of Education
- Lanzhou University
- Lanzhou 730000
| | - Zhipeng Zhang
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education
- Key Laboratory of Special Function Materials and Structure Design
- Ministry of Education
- Lanzhou University
- Lanzhou 730000
| | - You Li
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education
- Key Laboratory of Special Function Materials and Structure Design
- Ministry of Education
- Lanzhou University
- Lanzhou 730000
| | - Baorui Xia
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education
- Key Laboratory of Special Function Materials and Structure Design
- Ministry of Education
- Lanzhou University
- Lanzhou 730000
| | - Shoupeng Shi
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education
- Key Laboratory of Special Function Materials and Structure Design
- Ministry of Education
- Lanzhou University
- Lanzhou 730000
| | - Desheng Xue
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education
- Key Laboratory of Special Function Materials and Structure Design
- Ministry of Education
- Lanzhou University
- Lanzhou 730000
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20
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Ron A, Maniv E, Graf D, Park JH, Dagan Y. Anomalous magnetic ground state in an LaAlO3/SrTiO3 interface probed by transport through nanowires. PHYSICAL REVIEW LETTERS 2014; 113:216801. [PMID: 25479513 DOI: 10.1103/physrevlett.113.216801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Indexed: 06/04/2023]
Abstract
Resistance as a function of temperature down to 20 mK and magnetic fields up to 18 T for various carrier concentrations is measured for nanowires made from the SrTiO3/LaAlO3 interface using a hard mask shadow deposition technique. The narrow width of the wires (of the order of 50 nm) allows us to separate out the magnetic effects from the dominant superconducting ones at low magnetic fields. At this regime hysteresis loops are observed along with the superconducting transition. From our data analysis, we find that the magnetic order probed by the giant magnetoresistance effect vanishes at TCurie=954±20 mK. This order is not a simple ferromagnetic state but consists of domains with opposite magnetization having a preferred in-plane orientation.
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Affiliation(s)
- A Ron
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, Tel Aviv, 69978, Israel
| | - E Maniv
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, Tel Aviv, 69978, Israel
| | - D Graf
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
| | - J-H Park
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
| | - Y Dagan
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, Tel Aviv, 69978, Israel
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21
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Weston L, Cui XY, Ringer SP, Stampfl C. Density-functional prediction of a surface magnetic phase in SrTiO(3)/LaAlO(3) heterostructures induced by Al vacancies. PHYSICAL REVIEW LETTERS 2014; 113:186401. [PMID: 25396383 DOI: 10.1103/physrevlett.113.186401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2013] [Indexed: 06/04/2023]
Abstract
Based on first-principles density functional calculations we propose a novel Al vacancy induced ferromagnetism occurring at the LaAlO(3) surface of SrTiO(3)/LaAlO(3) bilayers. Magnetism at cation vacancies away from the surface is quenched due to charge compensation. Magnetic surface Al vacancies are stabilized due to the built-in electric field inside the LaAlO(3) region that raises the energy of the defect level, making charge compensation unfavorable. Surface Al vacancies prefer to form clusters and exhibit two-dimensional ferromagnetic alignment mediated by a long-range magnetic interaction. These results are discussed in light of recent experimental observations.
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Affiliation(s)
- L Weston
- School of Physics, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - X Y Cui
- Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, New South Wales 2006, Australia and School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - S P Ringer
- Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, New South Wales 2006, Australia and School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - C Stampfl
- School of Physics, The University of Sydney, Sydney, New South Wales 2006, Australia
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22
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Yu L, Zunger A. A polarity-induced defect mechanism for conductivity and magnetism at polar–nonpolar oxide interfaces. Nat Commun 2014; 5:5118. [DOI: 10.1038/ncomms6118] [Citation(s) in RCA: 230] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 09/02/2014] [Indexed: 11/09/2022] Open
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23
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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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24
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Bi F, Huang M, Ryu S, Lee H, Bark CW, Eom CB, Irvin P, Levy J. Room-temperature electronically-controlled ferromagnetism at the LaAlO3/SrTiO3 interface. Nat Commun 2014; 5:5019. [DOI: 10.1038/ncomms6019] [Citation(s) in RCA: 107] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Accepted: 08/20/2014] [Indexed: 11/09/2022] Open
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25
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Ganguli N, Kelly PJ. Tuning ferromagnetism at interfaces between insulating perovskite oxides. PHYSICAL REVIEW LETTERS 2014; 113:127201. [PMID: 25279639 DOI: 10.1103/physrevlett.113.127201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Indexed: 06/03/2023]
Abstract
We use density functional theory calculations to show that the LaAlO3|SrTiO3 interface between insulating perovskite oxides is borderline in satisfying the Stoner criterion for itinerant ferromagnetism and explore other oxide combinations with a view to satisfying it more amply. The larger lattice parameter of a LaScO3|BaTiO3 interface is found to be less favorable than the greater interface distortion of LaAlO3|CaTiO3. Compared to LaAlO3|SrTiO3, the latter is predicted to exhibit robust magnetism with a larger saturation moment and a higher Curie temperature. Our results provide support for a "two phase" picture of coexistent superconductivity and ferromagnetism.
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Affiliation(s)
- Nirmal Ganguli
- Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Paul J Kelly
- Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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26
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McKenzie I, Harada M, Kiefl RF, Levy CDP, MacFarlane WA, Morris GD, Ogata SI, Pearson MR, Sugiyama J. β-NMR measurements of lithium ion transport in thin films of pure and lithium-salt-doped poly(ethylene oxide). J Am Chem Soc 2014; 136:7833-6. [PMID: 24972297 DOI: 10.1021/ja503066a] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
β-Detected nuclear spin relaxation of (8)Li(+) has been used to study the microscopic diffusion of lithium ions in thin films of poly(ethylene oxide) (PEO), where the implanted lithium ions are present in extremely low concentration, and PEO with 30 wt % LiCF3SO3 over a wide range of temperatures both above and below the glass transition temperature. Recent measurements by Do et al. [Phys. Rev. Lett. 2013, 111, 018301] found that the temperature dependence of the Li(+) conductivity was identical to that of the dielectric α relaxation and was well described by the Vogel-Fulcher-Tammann relation, implying the α relaxation dominates the Li(+) transport process. In contrast, we find the hopping of Li(+) in both samples in the high temperature viscoelastic phase follows an Arrhenius law and depends significantly on the salt content. We propose that the hopping of Li(+) between cages involves motion of the polymer but that it is only for long-range diffusion where the α relaxation plays an important role.
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27
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28
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Lu HL, Liao ZM, Zhang L, Yuan WT, Wang Y, Ma XM, Yu DP. Reversible insulator-metal transition of LaAlO₃/SrTiO₃ interface for nonvolatile memory. Sci Rep 2013; 3:2870. [PMID: 24100438 PMCID: PMC3792417 DOI: 10.1038/srep02870] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Accepted: 09/19/2013] [Indexed: 11/12/2022] Open
Abstract
We report a new type of memory device based on insulating LaAlO3/SrTiO3 (LAO/STO) hetero-interface. The microstructures of the LAO/STO interface are characterized by Cs-corrected scanning transmission electron microscopy, which reveals the element intermixing at the interface. The inhomogeneous element distribution may result in carrier localization, which is responsible for the insulating state. The insulating state of such interface can be converted to metallic state by light illumination and the metallic state maintains after light off due to giant persistent photoconductivity (PPC) effect. The on/off ratio between the PPC and the initial dark conductance is as large as 105. The metallic state also can be converted back to insulating state by applying gate voltage. Reversible and reproducible resistive switching makes LAO/STO interface promising as a nonvolatile memory. Our results deepen the understanding of PPC phenomenon in LAO/STO, and pave the way for the development of all-oxide electronics integrating information storage devices.
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Affiliation(s)
- Hong-Liang Lu
- State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, P.R. China
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29
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Ball P. Material witness: Yet more layers. NATURE MATERIALS 2013; 12:785. [PMID: 23966051 DOI: 10.1038/nmat3742] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
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30
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Salluzzo M, Gariglio S, Stornaiuolo D, Sessi V, Rusponi S, Piamonteze C, De Luca GM, Minola M, Marré D, Gadaleta A, Brune H, Nolting F, Brookes NB, Ghiringhelli G. Origin of interface magnetism in BiMnO3/SrTiO3 and LaAlO3/SrTiO3 heterostructures. PHYSICAL REVIEW LETTERS 2013; 111:087204. [PMID: 24010471 DOI: 10.1103/physrevlett.111.087204] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2013] [Indexed: 06/02/2023]
Abstract
Possible ferromagnetism induced in otherwise nonmagnetic materials has been motivating intense research in complex oxide heterostructures. Here we show that a confined magnetism is realized at the interface between SrTiO3 and two insulating polar oxides, BiMnO3 and LaAlO3. By using polarization dependent x-ray absorption spectroscopy, we find that in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments. These local magnetic moments are associated with magnetic Ti3+ ions at the interface itself for LaAlO3/SrTiO3 and to Mn3+ ions in the overlayer for BiMnO3/SrTiO3. In LaAlO3/SrTiO3 the induced magnetism is quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon.
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Affiliation(s)
- M Salluzzo
- CNR-SPIN, Complesso MonteSantangelo via Cinthia, I-80126 Napoli, Italy
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31
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Lee JS, Xie YW, Sato HK, Bell C, Hikita Y, Hwang HY, Kao CC. Titanium dxy ferromagnetism at the LaAlO3/SrTiO3 interface. NATURE MATERIALS 2013; 12:703-706. [PMID: 23727948 DOI: 10.1038/nmat3674] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Accepted: 04/29/2013] [Indexed: 06/02/2023]
Abstract
A number of recent transport and magnetization studies have shown signs of ferromagnetism in the LaAlO3/SrTiO3 heterostructure, an unexpected property with no bulk analogue in the constituent materials. However, no experiment thus far has provided direct information on the host of the magnetism. Here we report spectroscopic investigations of the magnetism using element-specific techniques, including X-ray magnetic circular dichroism and X-ray absorption spectroscopy, along with corresponding model calculations. We find direct evidence for in-plane ferromagnetic order at the interface, with Ti(3+) character in the dxy orbital of the anisotropic t2g band. These findings establish a striking example of emergent phenomena at oxide interfaces.
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Affiliation(s)
- J-S Lee
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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32
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Gate-tunable polarized phase of two-dimensional electrons at the LaAlO3/SrTiO3 interface. Proc Natl Acad Sci U S A 2013; 110:9633-8. [PMID: 23708121 DOI: 10.1073/pnas.1221453110] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Controlling the coupling between localized spins and itinerant electrons can lead to exotic magnetic states. A novel system featuring local magnetic moments and extended 2D electrons is the interface between LaAlO3 and SrTiO3. The magnetism of the interface, however, was observed to be insensitive to the presence of these electrons and is believed to arise solely from extrinsic sources like oxygen vacancies and strain. Here we show the existence of unconventional electronic phases in the LaAlO3/SrTiO3 system pointing to an underlying tunable coupling between itinerant electrons and localized moments. Using anisotropic magnetoresistance and anomalous Hall effect measurements in a unique in-plane configuration, we identify two distinct phases in the space of carrier density and magnetic field. At high densities and fields, the electronic system is strongly polarized and shows a response, which is highly anisotropic along the crystalline directions. Surprisingly, below a density-dependent critical field, the polarization and anisotropy vanish whereas the resistivity sharply rises. The unprecedented vanishing of the easy axes below a critical field is in sharp contrast with other coupled magnetic systems and indicates strong coupling with the moments that depends on the symmetry of the itinerant electrons. The observed interplay between the two phases indicates the nature of magnetism at the LaAlO3/SrTiO3 interface as both having an intrinsic origin and being tunable.
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