1
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Minami S, Ikeda Y, Shimada T. Spontaneous Atomic-Scale Polar Skyrmions and Merons on a SrTiO 3 (001) Surface: Defect Engineering for Emerging Topological Orders. NANO LETTERS 2024; 24:3686-3693. [PMID: 38451549 DOI: 10.1021/acs.nanolett.3c05112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/08/2024]
Abstract
The emergence of nontrivial topological order in condensed matter has been attracting a great deal of attention owing to its promising technological applications in novel functional nanodevices. In ferroelectrics, the realization of polar topological order at an ultimately small scale is extremely challenging due to the lack of chiral interaction and the critical size of the ferroelectricity. Here, we break through these limitations and demonstrate that the ultimate atomic-scale polar skyrmion and meron (∼2 nm) can be induced by engineering oxygen vacancies on the SrTiO3 (001) surface based on first-principles calculations. The paraelectric-to-antiferrodistortive phase transition leads to a novel topological transition from skyrmion to meron, indicating phase-topology correlations. We also discuss accumulating and driving polar skyrmions based on the oxygen divacancy model; these results and the recent discovery of defect engineering techniques suggest the possibility of arithmetic operations on topological numbers through the natural self-organization and diffusion features of oxygen vacancies.
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Affiliation(s)
- Susumu Minami
- Department of Mechanical Engineering and Science, Kyoto University, Nishikyo-ku, Kyoto 615-8540, Japan
| | - Yoshitaka Ikeda
- Department of Mechanical Engineering and Science, Kyoto University, Nishikyo-ku, Kyoto 615-8540, Japan
| | - Takahiro Shimada
- Department of Mechanical Engineering and Science, Kyoto University, Nishikyo-ku, Kyoto 615-8540, Japan
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2
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Varignon J. Unexpected Competition between Ferroelectricity and Rashba Effects in Epitaxially Strained SrTiO_{3}. PHYSICAL REVIEW LETTERS 2024; 132:106401. [PMID: 38518324 DOI: 10.1103/physrevlett.132.106401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Accepted: 01/30/2024] [Indexed: 03/24/2024]
Abstract
The Rashba parameter α_{R} is usually assumed to scale linearly with the amplitude of polar displacements by construction of the spin-orbit interaction. On the basis of first-principles simulations, ferroelectric phases of SrTiO_{3} reached under epitaxial compressive strain are characterized by (i) large Rashba effects at the bottom of the conduction band near the paraelectric-ferroelectric boundary and (ii) an unexpected suppression of the phenomena when the amplitude of polar displacements increases. This peculiar behavior is ascribed to the inverse dependence of the Rashba parameter with the crystal field Δ_{CF} induced by the polar displacements that alleviates the degeneracy of Ti t_{2g} states and annihilates the Rashba effects. Although α_{R} has intrinsically a linear dependance on polar displacements, the latter becomes antagonist to Rashba phenomena at large polar mode amplitude. Thus, the Rashba coefficient may be bound to an upper value.
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Affiliation(s)
- Julien Varignon
- CRISMAT, ENSICAEN, Normandie Université, UNICAEN, CNRS, 14000 Caen, France
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3
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Song C, Yang Q, Liu X, Zhao H, Zhang C, Meng S. Electronic Origin of Laser-Induced Ferroelectricity in SrTiO 3. J Phys Chem Lett 2023; 14:576-583. [PMID: 36633437 DOI: 10.1021/acs.jpclett.2c03078] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Although ultrafast control of the nonthermally driven ferroelectric transition of paraelectric SrTiO3 was achieved under laser excitation, the underlying mechanism and dynamics of the photoinduced phase transition remain ambiguous. Here, the determinant formation mechanism of ultrafast ferroelectricity in SrTiO3 is traced by nonadiabatic dynamics simulations. That is, the selective excitation of multiple phonons, induced by photoexcited electrons through the strong correlation between electronic excitation and lattice distortion, results in the breaking of the crystal central symmetry and the onset of ferroelectricity. The accompanying population transition between 3dz2 and 3dx2-y2 orbitals excites multiple phonon branches, including the two high-energy longitudinal optical modes, so as to drive the titanium ion away from the center of the oxygen octahedron and generate a metastable ferroelectric phase. Our findings reveal a cooperative electronic and ionic driving mechanism for the laser-induced ferroelectricity that provides new schemes for the optical control of ultrafast quantum states.
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Affiliation(s)
- Chenchen Song
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing100049, China
| | - Qing Yang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing100190, China
| | - Xinbao Liu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing100049, China
| | - Hui Zhao
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing100049, China
| | - Cui Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing100190, China
- Songshan Lake Materials Laboratory, Dongguan523808, China
| | - Sheng Meng
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing100049, China
- Songshan Lake Materials Laboratory, Dongguan523808, China
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4
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Talanov MV, Stash AI, Ivanov SA, Zhukova ES, Gorshunov BP, Nekrasov BM, Stolyarov VS, Kozlov VI, Savinov M, Bush AA. Octahedra-Tilted Control of Displacement Disorder and Dielectric Relaxation in Mn-Doped SrTiO 3 Single Crystals. J Phys Chem Lett 2022; 13:11720-11728. [PMID: 36512678 DOI: 10.1021/acs.jpclett.2c03513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Strontium titanate SrTiO3 (STO) is a canonical example of a quantum paraelectric, and its doping with manganese ions unlocks its potential as a quantum multiferroic candidate. However, to date, the specifics of incorporation of the manganese ion into the perovskite lattice and its impact on structure-property relationships are debatable questions. Herein, using high-precision X-ray diffraction of a Mn (2 atom %)-doped STO single crystal, clear fingerprints of the displacement disorder of Mn cations in the perovskite B-sublattice are observed. Moreover, near the temperature of the antiferrodistortive transition, the off-center Mn position splits in two, providing the unequal potential barrier's distribution for possible local atomic hopping. A link with this was found via analysis of the dielectric response that reveals two Arrhenius-type relaxation processes with similar activation energies (35 and 43 meV) and attempt frequencies (1 × 1011 and ∼1.6 × 1010 Hz), suggesting similar dielectric relaxation mechanisms.
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Affiliation(s)
- Mikhail V Talanov
- Research Institute of Physics, Southern Federal University, 194 Stachki av., 344090Rostov-on-Don, Russia
| | - Adam I Stash
- A. N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Science, 28 Vavilov Strasse, 119991Moscow, Russia
| | - Sergey A Ivanov
- Chemical Department, Moscow State University, 1 Leninskie Gory, 119991Moscow, Russia
| | - Elena S Zhukova
- Laboratory of Terahertz Spectroscopy, Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology (National Research University), 9 Institutskiy Pereulok, Dolgoprudny, Moscow Region141700, Russia
| | - Boris P Gorshunov
- Laboratory of Terahertz Spectroscopy, Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology (National Research University), 9 Institutskiy Pereulok, Dolgoprudny, Moscow Region141700, Russia
| | - Boris M Nekrasov
- Laboratory of Terahertz Spectroscopy, Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology (National Research University), 9 Institutskiy Pereulok, Dolgoprudny, Moscow Region141700, Russia
| | - Vasily S Stolyarov
- Center for Advanced Mesoscience and Nanotechnology, Moscow Institute of Physics and Technology (National Research University), 9 Institutskiy Pereulok, Dolgoprudny, Moscow Region141700, Russia
| | - Vladislav I Kozlov
- Research Institute of Solid-State Electronics Materials, MIREA - Russian Technological University (RTU MIREA), 78 Vernadsky prospect, 119454Moscow, Russia
- Kapitza Institute for Physical Problems RAS, 2 st. Kosygina, 119334Moscow, Russia
| | - Maxim Savinov
- Institute of Physics, Czech Academy of Sciences, 18200Prague 8, Czech Republic
| | - Alexander A Bush
- Research Institute of Solid-State Electronics Materials, MIREA - Russian Technological University (RTU MIREA), 78 Vernadsky prospect, 119454Moscow, Russia
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5
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Shin D, Latini S, Schäfer C, Sato SA, Baldini E, De Giovannini U, Hübener H, Rubio A. Simulating Terahertz Field-Induced Ferroelectricity in Quantum Paraelectric SrTiO_{3}. PHYSICAL REVIEW LETTERS 2022; 129:167401. [PMID: 36306771 DOI: 10.1103/physrevlett.129.167401] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Revised: 04/19/2022] [Accepted: 09/01/2022] [Indexed: 06/16/2023]
Abstract
Recent experiments have demonstrated that light can induce a transition from the quantum paraelectric to the ferroelectric phase of SrTiO_{3}. Here, we investigate this terahertz field-induced ferroelectric phase transition by solving the time-dependent lattice Schrödinger equation based on first-principles calculations. We find that ferroelectricity originates from a light-induced mixing between ground and first excited lattice states in the quantum paraelectric phase. In agreement with the experimental findings, our study shows that the nonoscillatory second harmonic generation signal can be evidence of ferroelectricity in SrTiO_{3}. We reveal the microscopic details of this exotic phase transition and highlight that this phenomenon is a unique behavior of the quantum paraelectric phase.
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Affiliation(s)
- Dongbin Shin
- Max Planck Institute for the Structure and Dynamics of Matter and Center for Free Electron Laser Science, 22761 Hamburg, Germany
| | - Simone Latini
- Max Planck Institute for the Structure and Dynamics of Matter and Center for Free Electron Laser Science, 22761 Hamburg, Germany
| | - Christian Schäfer
- Max Planck Institute for the Structure and Dynamics of Matter and Center for Free Electron Laser Science, 22761 Hamburg, Germany
- Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, 412 96 Göteborg, Sweden
| | - Shunsuke A Sato
- Max Planck Institute for the Structure and Dynamics of Matter and Center for Free Electron Laser Science, 22761 Hamburg, Germany
- Center for Computational Sciences, University of Tsukuba, Tsukuba 305-8577, Japan
| | - Edoardo Baldini
- Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
| | - Umberto De Giovannini
- Max Planck Institute for the Structure and Dynamics of Matter and Center for Free Electron Laser Science, 22761 Hamburg, Germany
- Universitá degli Studi di Palermo, Dipartimento di Fisica e Chimica-Emilio Segrè, via Archirafi 36, I-90123 Palermo, Italy
| | - Hannes Hübener
- Max Planck Institute for the Structure and Dynamics of Matter and Center for Free Electron Laser Science, 22761 Hamburg, Germany
| | - Angel Rubio
- Max Planck Institute for the Structure and Dynamics of Matter and Center for Free Electron Laser Science, 22761 Hamburg, Germany
- Nano-Bio Spectroscopy Group, Departamento de Fisica de Materiales, Universidad del País Vasco UPV/EHU, 20018 San Sebastián, Spain
- Center for Computational Quantum Physics (CCQ), The Flatiron Institute, 162 Fifth Avenue, New York, New York 10010, USA
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6
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Pressure-driven ferroelectric phase transition for the Pnma-CsPbBr3: Mechanical and dynamical stability study. J SOLID STATE CHEM 2022. [DOI: 10.1016/j.jssc.2022.123402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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7
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Abstract
In recent decades, the behavior of SrTiO3 upon annealing in reducing conditions has been under intense academic scrutiny. Classically, its conductivity can be described using point defect chemistry and predicting n-type or p-type semiconducting behavior depending on oxygen activity. In contrast, many examples of metallic behavior induced by thermal reduction have recently appeared in the literature, challenging this established understanding. In this study, we aim to resolve this contradiction by demonstrating that an initially insulating, as-received SrTiO3 single crystal can indeed be reduced to a metallic state, and is even stable against room temperature reoxidation. However, once the sample has been oxidized at a high temperature, subsequent reduction can no longer be used to induce metallic behavior, but semiconducting behavior in agreement with the predictions of point defect chemistry is observed. Our results indicate that the dislocation-rich surface layer plays a decisive role and that its local chemical composition can be changed depending on annealing conditions. This reveals that the prediction of the macroscopic electronic properties of SrTiO3 is a highly complex task, and not only the current temperature and oxygen activity but also the redox history play an important role.
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8
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Han B, Zhu R, Li X, Wu M, Ishikawa R, Feng B, Bai X, Ikuhara Y, Gao P. Two-Dimensional Room-Temperature Giant Antiferrodistortive SrTiO_{3} at a Grain Boundary. PHYSICAL REVIEW LETTERS 2021; 126:225702. [PMID: 34152191 DOI: 10.1103/physrevlett.126.225702] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 04/23/2021] [Indexed: 06/13/2023]
Abstract
The broken symmetry at structural defects such as grain boundaries (GBs) discontinues chemical bonds, leading to the emergence of new properties that are absent in the bulk owing to the couplings between the lattice and other parameters. Here, we create a two-dimensional antiferrodistortive (AFD) strontium titanate (SrTiO_{3}) phase at a Σ13(510)/[001] SrTiO_{3} tilt GB at room temperature. We find that such an anomalous room-temperature AFD phase with the thickness of approximate six unit cells is stabilized by the charge doping from oxygen vacancies. The localized AFD originated from the strong lattice-charge couplings at a SrTiO_{3} GB is expected to play important roles in the electrical and optical activity of GBs and can explain past experiments such as the transport properties of electroceramic SrTiO_{3}. Our study also provides new strategies to create low-dimensional anomalous elements for future nanoelectronics via grain boundary engineering.
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Affiliation(s)
- Bo Han
- Electron Microscopy Laboratory and International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Ruixue Zhu
- Electron Microscopy Laboratory and International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Xiaomei Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Mei Wu
- Electron Microscopy Laboratory and International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Ryo Ishikawa
- Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan
- Japan Science and Technology Agency, PRESTO, Kawaguchi, Saitama 332-0012, Japan
| | - Bin Feng
- Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan
| | - Xuedong Bai
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Yuichi Ikuhara
- Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan
- Nanostructures Research Laboratory, Japan Fine Ceramic Center, Nagoya 456-8587, Japan
- WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Peng Gao
- Electron Microscopy Laboratory and International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
- Interdisciplinary Institute of Light-Element Quantum Materials and Research Center for Light-Element Advanced Materials, Peking University, Beijing 100871, China
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9
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Min T, Choi W, Seo J, Han G, Song K, Ryu S, Lee H, Lee J, Eom K, Eom CB, Jeong HY, Kim YM, Lee J, Oh SH. Cooperative evolution of polar distortion and nonpolar rotation of oxygen octahedra in oxide heterostructures. SCIENCE ADVANCES 2021; 7:7/17/eabe9053. [PMID: 33883134 PMCID: PMC8059930 DOI: 10.1126/sciadv.abe9053] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Accepted: 03/05/2021] [Indexed: 05/23/2023]
Abstract
Polarity discontinuity across LaAlO3/SrTiO3 (LAO/STO) heterostructures induces electronic reconstruction involving the formation of two-dimensional electron gas (2DEG) and structural distortions characterized by antiferrodistortive (AFD) rotation and ferroelectric (FE) distortion. We show that AFD and FE modes are cooperatively coupled in LAO/STO (111) heterostructures; they coexist below the critical thickness (t c) and disappear simultaneously above t c with the formation of 2DEG. Electron energy-loss spectroscopy and density functional theory (DFT) calculations provide direct evidence of oxygen vacancy (V O) formation at the LAO (111) surface, which acts as the source of 2DEG. Tracing the AFD rotation and FE distortion of LAO reveals that their evolution is strongly correlated with V O distribution. The present study demonstrates that AFD and FE modes in oxide heterostructures emerge as a consequence of interplay between misfit strain and polar field, and further that their combination can be tuned to competitive or cooperative coupling by changing the interface orientation.
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Affiliation(s)
- Taewon Min
- Department of Physics, Pusan National University, Busan 46241, Republic of Korea
| | - Wooseon Choi
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Jinsol Seo
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Gyeongtak Han
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Kyung Song
- Materials Testing and Reliability Division, Korea Institute of Materials Science (KIMS), Changwon 51508, Republic of Korea
| | - Sangwoo Ryu
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Hyungwoo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Jungwoo Lee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Kitae Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Chang-Beom Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Hu Young Jeong
- UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea
| | - Young-Min Kim
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea.
| | - Jaekwang Lee
- Department of Physics, Pusan National University, Busan 46241, Republic of Korea.
| | - Sang Ho Oh
- Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea.
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10
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Zhang Y, Wang J, Ghosez P. Unraveling the Suppression of Oxygen Octahedra Rotations in A_{3}B_{2}O_{7} Ruddlesden-Popper Compounds: Engineering Multiferroicity and Beyond. PHYSICAL REVIEW LETTERS 2020; 125:157601. [PMID: 33095620 DOI: 10.1103/physrevlett.125.157601] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Accepted: 08/11/2020] [Indexed: 06/11/2023]
Abstract
The competition between polar distortions and BO_{6} octahedra rotations is well known to be critical in explaining the ground state of various ABO_{3} perovskites. Here, we show from first-principles calculations that a similar competition between interlayer rumpling and rotations is playing a key role in layered Ruddlesden-Popper (RP) perovskites. This competition explains the suppression of oxygen octahedra rotations and hybrid improper ferroelectricity in A_{3}B_{2}O_{7} compounds with rare-earth ions in the rocksalt layer and also appears relevant to other phenomena like negative thermal expansion and the dimensionality determined band gap in RP systems. Moreover, we highlight that RP perovskites offer more flexibility than ABO_{3} perovskites in controlling such a competition and four distinct strategies are proposed to tune it. These strategies are shown to be promising for designing new multiferroics. They are generic and might also be exploited for tuning negative thermal expansion and band gap.
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Affiliation(s)
- Yajun Zhang
- Theoretical Materials Physics, Q-MAT, CESAM, Université de Liège, B-4000 Liège, Belgium
- Department of Engineering Mechanics and Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Zhejiang University, 38 Zheda Road, Hangzhou 310027, China
| | - Jie Wang
- Department of Engineering Mechanics and Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Zhejiang University, 38 Zheda Road, Hangzhou 310027, China
| | - Philippe Ghosez
- Theoretical Materials Physics, Q-MAT, CESAM, Université de Liège, B-4000 Liège, Belgium
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11
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Baker JS, Bowler DR. Polar Morphologies from First Principles: PbTiO
3
Films on SrTiO
3
Substrates and the p(2×Λ) Surface Reconstruction. ADVANCED THEORY AND SIMULATIONS 2020. [DOI: 10.1002/adts.202000154] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Jack S. Baker
- London Centre for Nanotechnology UCL 17‐19 Gordon St London WC1H 0AH UK
- Department of Physics & Astronomy UCL Gower St London WC1E 6BT UK
| | - David R. Bowler
- London Centre for Nanotechnology UCL 17‐19 Gordon St London WC1H 0AH UK
- Department of Physics & Astronomy UCL Gower St London WC1E 6BT UK
- International Centre for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) 1‐1 Namiki Tsukuba Ibaraki 305‐0044 Japan
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12
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Din NU, Jiang T, Gholam-Mirzaei S, Chini M, Turkowski V. Electron-electron correlations and structural, spectral and polarization properties of tetragonal BaTiO 3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:475601. [PMID: 32726762 DOI: 10.1088/1361-648x/abaa81] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Accepted: 07/29/2020] [Indexed: 06/11/2023]
Abstract
To analyze the role of electron-electron correlation effects in structural (local-geometry), spectral and polarization properties of tetragonal BaTiO3we apply DFT +Uapproach. We demonstrate that the system properties drastically change when the value of the local Coulomb repulsionUcrosses the critical valueUc≈ 7 eV. In particular, the correlation effects cause a change of the ratio of the in-plane and inter-plane Ti-O bond lengths, which results in a flip of the order of the Tid-bands and change of the polarizability of the system. Since the consensus value ofUin BaTiO3is unknown, we discuss how the obtained results may be revealed in experimental data, especially in the optical response and ultrafast charge dynamics, where effectiveUis dynamically tuned.
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Affiliation(s)
- Naseem Ud Din
- Department of Physics, University of Central Florida, Orlando, FL 32816, United States of America
| | - Tao Jiang
- Department of Physics, University of Central Florida, Orlando, FL 32816, United States of America
| | - Shima Gholam-Mirzaei
- Department of Physics, University of Central Florida, Orlando, FL 32816, United States of America
| | - Michael Chini
- Department of Physics, University of Central Florida, Orlando, FL 32816, United States of America
| | - Volodymyr Turkowski
- Department of Physics, University of Central Florida, Orlando, FL 32816, United States of America
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13
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He X, Bansal D, Winn B, Chi S, Boatner L, Delaire O. Anharmonic Eigenvectors and Acoustic Phonon Disappearance in Quantum Paraelectric SrTiO_{3}. PHYSICAL REVIEW LETTERS 2020; 124:145901. [PMID: 32338961 DOI: 10.1103/physrevlett.124.145901] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 01/19/2020] [Accepted: 03/16/2020] [Indexed: 06/11/2023]
Abstract
Pronounced anomalies in the SrTiO_{3} dynamical structure factor, S(Q,E), including the disappearance of acoustic phonon branches at low temperatures, were uncovered with inelastic neutron scattering (INS) and simulations. The striking effect reflects anharmonic couplings between acoustic and optic phonons and the incipient ferroelectric instability near the quantum critical point. It is rationalized using a first-principles renormalized anharmonic phonon approach, pointing to nonlinear Ti-O hybridization causing unusual changes in real-space phonon eigenvectors, frequencies, group velocities, and scattering phase space. Our method is general and establishes how T dependences beyond the harmonic regime, assessed by INS mapping of large reciprocal-space volumes, provide real-space insights into anharmonic atomic dynamics near phase transitions.
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Affiliation(s)
- Xing He
- Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA
| | - Dipanshu Bansal
- Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra 400076, India
| | - Barry Winn
- Neutron Scattering Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Songxue Chi
- Neutron Scattering Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Lynn Boatner
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Olivier Delaire
- Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA
- Department of Physics, Duke University, Durham, North Carolina 27708, USA
- Department of Chemistry, Duke University, Durham, North Carolina 27708, USA
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14
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Wu YN, Saidi WA, Wuenschell JK, Tadano T, Ohodnicki P, Chorpening B, Duan Y. Anharmonicity Explains Temperature Renormalization Effects of the Band Gap in SrTiO 3. J Phys Chem Lett 2020; 11:2518-2523. [PMID: 32163705 DOI: 10.1021/acs.jpclett.0c00183] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Soft phonon modes in strongly anharmonic crystals are often neglected in calculations of phonon-related properties. Herein, we experimentally measure the temperature effects on the band gap of cubic SrTiO3, and compare with first-principles calculations by accounting for electron-phonon coupling using harmonic and anharmonic phonon modes. The harmonic phonon modes show an increase in the band gap with temperature using either Allen-Heine-Cardona theory or finite-displacement approach, and with semilocal or hybrid exchange-correlation functionals. This finding is in contrast with experimental results that show a decrease in the band gap with temperature. We show that the disagreement can be rectified by using anharmonic phonon modes that modify the contributions not only from the significantly corrected soft modes, but also from the modes that show little correction in frequencies. Our results confirm the importance of soft-phonon modes that are often neglected in the computation of phonon-related properties and particularly in electron-phonon coupling.
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Affiliation(s)
- Yu-Ning Wu
- National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States
| | - Wissam A Saidi
- National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States
| | - Jeffrey K Wuenschell
- National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States
- Leidos Research Support Team, Pittsburgh, Pennsylvania 15236, United States
| | - Terumasa Tadano
- Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
| | - Paul Ohodnicki
- National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States
| | - Benjamin Chorpening
- National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States
| | - Yuhua Duan
- National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States
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15
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Nova TF, Disa AS, Fechner M, Cavalleri A. Metastable ferroelectricity in optically strained SrTiO 3. Science 2020; 364:1075-1079. [PMID: 31197010 DOI: 10.1126/science.aaw4911] [Citation(s) in RCA: 107] [Impact Index Per Article: 26.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2018] [Accepted: 05/20/2019] [Indexed: 11/03/2022]
Abstract
Fluctuating orders in solids are generally considered high-temperature precursors of broken symmetry phases. However, in some cases, these fluctuations persist to zero temperature and prevent the emergence of long-range order. Strontium titanate (SrTiO3) is a quantum paraelectric in which dipolar fluctuations grow upon cooling, although a long-range ferroelectric order never sets in. Here, we show that optical excitation of lattice vibrations can induce polar order. This metastable polar phase, observed up to temperatures exceeding 290 kelvin, persists for hours after the optical pump is interrupted. Furthermore, hardening of a low-frequency vibration points to a photoinduced ferroelectric phase transition, with a spatial domain distribution suggestive of a photoflexoelectric coupling.
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Affiliation(s)
- T F Nova
- Max Planck Institute for the Structure and Dynamics of Matter, Hamburg 22761, Germany. .,The Hamburg Centre for Ultrafast Imaging, Hamburg 22761, Germany
| | - A S Disa
- Max Planck Institute for the Structure and Dynamics of Matter, Hamburg 22761, Germany
| | - M Fechner
- Max Planck Institute for the Structure and Dynamics of Matter, Hamburg 22761, Germany
| | - A Cavalleri
- Max Planck Institute for the Structure and Dynamics of Matter, Hamburg 22761, Germany. .,The Hamburg Centre for Ultrafast Imaging, Hamburg 22761, Germany.,Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, United Kingdom
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16
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Li X, Qiu T, Zhang J, Baldini E, Lu J, Rappe AM, Nelson KA. Terahertz field-induced ferroelectricity in quantum paraelectric SrTiO 3. Science 2020; 364:1079-1082. [PMID: 31197011 DOI: 10.1126/science.aaw4913] [Citation(s) in RCA: 114] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2018] [Accepted: 05/20/2019] [Indexed: 11/02/2022]
Abstract
"Hidden phases" are metastable collective states of matter that are typically not accessible on equilibrium phase diagrams. These phases can host exotic properties in otherwise conventional materials and hence may enable novel functionality and applications, but their discovery and access are still in early stages. Using intense terahertz electric field excitation, we found that an ultrafast phase transition into a hidden ferroelectric phase can be dynamically induced in quantum paraelectric strontium titanate (SrTiO3). The induced lowering in crystal symmetry yields substantial changes in the phonon excitation spectra. Our results demonstrate collective coherent control over material structure, in which a single-cycle field drives ions along the microscopic pathway leading directly to their locations in a new crystalline phase on an ultrafast time scale.
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Affiliation(s)
- Xian Li
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Tian Qiu
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Jiahao Zhang
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Edoardo Baldini
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Jian Lu
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Andrew M Rappe
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Keith A Nelson
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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17
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Li X, Fauqué B, Zhu Z, Behnia K. Phonon Thermal Hall Effect in Strontium Titanate. PHYSICAL REVIEW LETTERS 2020; 124:105901. [PMID: 32216396 DOI: 10.1103/physrevlett.124.105901] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 02/20/2020] [Indexed: 06/10/2023]
Abstract
It has been known for more than a decade that phonons can produce an off-diagonal thermal conductivity in the presence of a magnetic field. Recent studies of thermal Hall conductivity, κ_{xy}, in a variety of contexts, however, have assumed a negligibly small phonon contribution. We present a study of κ_{xy} in quantum paraelectric SrTiO_{3}, which is a nonmagnetic insulator and find that its peak value exceeds what has been reported in any other insulator, including those in which the signal has been qualified as "giant." Remarkably, κ_{xy}(T) and κ(T) peak at the same temperature and the former decreases faster than the latter at both sides of the peak. Interestingly, in the case of La_{2}CuO_{4} and α-RuCl_{3}, κ_{xy}(T) and κ(T) peak also at the same temperature. We also studied KTaO_{3} and found a small signal, indicating that a sizable κ_{xy}(T) is not a generic feature of quantum paraelectrics. Combined to other observations, this points to a crucial role played by antiferrodistortive domains in generating κ_{xy} of this solid.
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Affiliation(s)
- Xiaokang Li
- Laboratoire de Physique et d'Etude des Matériaux (CNRS) ESPCI Paris, PSL Research University, 75005 Paris, France
- Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Benoît Fauqué
- JEIP, USR 3573 CNRS, Collège de France, PSL University, 11, place Marcelin Berthelot, 75231 Paris Cedex 05, France
| | - Zengwei Zhu
- Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Kamran Behnia
- Laboratoire de Physique et d'Etude des Matériaux (CNRS) ESPCI Paris, PSL Research University, 75005 Paris, France
- II. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany
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18
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Interface polarization model for a 2-dimensional electron gas at the BaSnO 3/LaInO 3 interface. Sci Rep 2019; 9:16202. [PMID: 31700133 PMCID: PMC6838460 DOI: 10.1038/s41598-019-52772-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Accepted: 10/22/2019] [Indexed: 11/23/2022] Open
Abstract
In order to explain the experimental sheet carrier density n2D at the interface of BaSnO3/LaInO3, we consider a model that is based on the presence of interface polarization in LaInO3 which extends over 2 pseudocubic unit cells from the interface and eventually disappears in the next 2 unit cells. Considering such interface polarization in calculations based on 1D Poisson-Schrödinger equations, we consistently explain the dependence of the sheet carrier density of BaSnO3/LaInO3 heterinterfaces on the thickness of the LaInO3 layer and the La doping of the BaSnO3 layer. Our model is supported by a quantitative analysis of atomic position obtained from high resolution transmission electron microscopy which evidences suppression of the octahedral tilt and a vertical lattice expansion in LaInO3 over 2–3 pseudocubic unit cells at the coherently strained interface.
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19
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Behnia K, Kapitulnik A. A lower bound to the thermal diffusivity of insulators. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:405702. [PMID: 31252425 DOI: 10.1088/1361-648x/ab2db6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
It has been known for decades that thermal conductivity of insulating crystals becomes proportional to the inverse of temperature when the latter is comparable to, or higher than, the Debye temperature. This behavior has been understood as resulting from Umklapp scattering among phonons. We put under scrutiny the magnitude of the thermal diffusion constant in this regime and find that it does not fall below a threshold set by the square of sound velocity times the Planckian time ([Formula: see text]). The conclusion, based on scrutinizing the ratio in cubic crystals with high thermal resistivity, appears to hold even in glasses where Umklapp events are not conceivable. Explaining this boundary, reminiscent of a recently-noticed limit for charge transport in metals, is a challenge to theory.
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Affiliation(s)
- Kamran Behnia
- Laboratoire Physique et Etude de Matériaux (CNRS-Sorbonne Université), ESPCI Paris, PSL Research University, 75005 Paris, France. II. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany
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20
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Tomioka Y, Shirakawa N, Shibuya K, Inoue IH. Enhanced superconductivity close to a non-magnetic quantum critical point in electron-doped strontium titanate. Nat Commun 2019; 10:738. [PMID: 30760712 PMCID: PMC6374393 DOI: 10.1038/s41467-019-08693-1] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Accepted: 01/25/2019] [Indexed: 11/24/2022] Open
Abstract
Studies on quantum critical points (QCP) have focused on magnetic QCPs to date. Remarkable phenomena such as superconductivity due to avoided criticality have been discovered, but we focus here on the non-magnetic counterpart, i.e., the superconductivity of SrTiO3 regarded as being close to a ferroelectric QCP. Here we prepare high-quality Sr1-xLaxTi(16O1-z18Oz)3 single crystals without localisation at low temperatures, which allow us to systematically investigate the La substitution of Sr as an alternative to introducing oxygen vacancies. Analysis of our data based on a theoretical model predicts an appearance of the ferroelectric QCP around 3 × 1018 cm-3. Because of the QCP, the superconducting dome of Sr1-xLaxTiO3 can be raised upwards. Furthermore, remarkable enhancement of Tc (~0.6 K) is achieved by 18O exchange on the Sr1-xLaxTiO3 crystals. These findings provide a new knob for observing intriguing physics around the ferroelectric QCP.
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Affiliation(s)
- Yasuhide Tomioka
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8565, Japan.
| | - Naoki Shirakawa
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8565, Japan
| | - Keisuke Shibuya
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8565, Japan
| | - Isao H Inoue
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8565, Japan.
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21
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Morales A, Zupancic P, Léonard J, Esslinger T, Donner T. Coupling two order parameters in a quantum gas. NATURE MATERIALS 2018; 17:686-690. [PMID: 29967462 DOI: 10.1038/s41563-018-0118-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2017] [Accepted: 05/24/2018] [Indexed: 06/08/2023]
Abstract
Controlling matter to simultaneously support coupled properties is of fundamental and technological importance1 (for example, in multiferroics2-5 or high-temperature superconductors6-9). However, determining the microscopic mechanisms responsible for the simultaneous presence of different orders is difficult, making it hard to predict material phenomenology10,11 or modify properties12-16. Here, using a quantum gas to engineer an adjustable interaction at the microscopic level, we demonstrate scenarios of competition, coexistence and mutual enhancement of two orders. For the enhancement scenario, the presence of one order lowers the critical point of the other. Our system is realized by a Bose-Einstein condensate that can undergo self-organization phase transitions in two optical resonators17, resulting in two distinct crystalline density orders. We characterize the coupling between these orders by measuring the composite order parameter and the elementary excitations and explain our results with a mean-field free-energy model derived from a microscopic Hamiltonian. Our system is ideally suited to explore quantum tricritical points18 and can be extended to study the interplay of spin and density orders19 as a function of temperature20.
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Affiliation(s)
- Andrea Morales
- Institute for Quantum Electronics, ETH Zurich, Zurich, Switzerland
| | - Philip Zupancic
- Institute for Quantum Electronics, ETH Zurich, Zurich, Switzerland
| | - Julian Léonard
- Institute for Quantum Electronics, ETH Zurich, Zurich, Switzerland
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Tilman Esslinger
- Institute for Quantum Electronics, ETH Zurich, Zurich, Switzerland.
| | - Tobias Donner
- Institute for Quantum Electronics, ETH Zurich, Zurich, Switzerland
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22
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Gu T, Scarbrough T, Yang Y, Íñiguez J, Bellaiche L, Xiang HJ. Cooperative Couplings between Octahedral Rotations and Ferroelectricity in Perovskites and Related Materials. PHYSICAL REVIEW LETTERS 2018; 120:197602. [PMID: 29799252 DOI: 10.1103/physrevlett.120.197602] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Revised: 01/18/2018] [Indexed: 06/08/2023]
Abstract
The structure of ABO_{3} perovskites is dominated by two types of unstable modes, namely, the oxygen octahedral rotation (AFD) and ferroelectric (FE) mode. It is generally believed that such AFD and FE modes tend to compete and suppress each other. Here we use first-principles methods to show that a dual nature of the FE-AFD coupling, which turns from competitive to cooperative as the AFD mode strengthens, occurs in numerous perovskite oxides. We provide a unified model of such a dual interaction by introducing novel high-order coupling terms and explain the atomistic origin of the resulting new form of ferroelectricity in terms of universal steric mechanisms. We also predict that such a novel form of ferroelectricity leads to atypical behaviors, such as an enhancement of all the three Cartesian components of the electric polarization under hydrostatic pressure and compressive epitaxial strain.
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Affiliation(s)
- Teng Gu
- Key Laboratory of Computational Physical Sciences (Ministry of Education), State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433, People's Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China
| | - Timothy Scarbrough
- Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - Yurong Yang
- Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - Jorge Íñiguez
- Materials Research and Technology Department, Luxembourg Institute of Science and Technology (LIST), 41 Rue du Brill, L-4422 Belvaux, Luxembourg
| | - L Bellaiche
- Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - H J Xiang
- Key Laboratory of Computational Physical Sciences (Ministry of Education), State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433, People's Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China
- Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA
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23
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Martelli V, Jiménez JL, Continentino M, Baggio-Saitovitch E, Behnia K. Thermal Transport and Phonon Hydrodynamics in Strontium Titanate. PHYSICAL REVIEW LETTERS 2018; 120:125901. [PMID: 29694090 DOI: 10.1103/physrevlett.120.125901] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2017] [Indexed: 05/02/2023]
Abstract
We present a study of thermal conductivity, κ, in undoped and doped strontium titanate in a wide temperature range (2-400 K) and detecting different regimes of heat flow. In undoped SrTiO_{3}, κ evolves faster than cubic with temperature below its peak and in a narrow temperature window. Such behavior, previously observed in a handful of solids, has been attributed to a Poiseuille flow of phonons, expected to arise when momentum-conserving scattering events outweigh momentum-degrading ones. The effect disappears in the presence of dopants. In SrTi_{1-x}Nb_{x}O_{3}, a significant reduction in lattice thermal conductivity starts below the temperature at which the average inter-dopant distance and the thermal wavelength of acoustic phonons become comparable. In the high-temperature regime, thermal diffusivity becomes proportional to the inverse of temperature, with a prefactor set by sound velocity and Planckian time (τ_{p}=(ℏ/k_{B}T)).
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Affiliation(s)
- Valentina Martelli
- Centro Brasileiro de Pesquisas Físicas, 22290-180 Rio de Janeiro, Rio de Janeiro, Brazil
| | - Julio Larrea Jiménez
- Institute of Physics, University of São Paulo, CEP 05508-090 São Paulo, São Paulo, Brazil
| | - Mucio Continentino
- Centro Brasileiro de Pesquisas Físicas, 22290-180 Rio de Janeiro, Rio de Janeiro, Brazil
| | | | - Kamran Behnia
- Laboratoire Physique et Etude de Matériaux (CNRS-UPMC), ESPCI Paris, PSL Research University, 75005 Paris, France
- II. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany
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24
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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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25
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Vonrüti N, Aschauer U. Anion Order and Spontaneous Polarization in LaTiO_{2}N Oxynitride Thin Films. PHYSICAL REVIEW LETTERS 2018; 120:046001. [PMID: 29437439 DOI: 10.1103/physrevlett.120.046001] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Indexed: 06/08/2023]
Abstract
The perovskite oxynitride LaTiO_{2}N is a promising material for photocatalytic water splitting under visible light. One of the obstacles towards higher efficiencies of this and similar materials stems from charge-carrier recombination, which could be suppressed by the surface charges resulting from the dipolar field in polar materials. In this study, we investigate the spontaneous polarization in epitaxially strained LaTiO_{2}N thin films via density functional theory calculations. The effect of epitaxial strain on the anion order, resulting out-of-plane polarization, energy barriers for polarization reversal, and corresponding coercive fields are studied. We find that for compressive strains larger than 4% the thermodynamically stable anion order is polar along the out-of-plane direction and has a coercive field comparable to other switchable ferroelectrics. Our results show that strained LaTiO_{2}N could indeed suppress carrier recombination and lead to enhanced photocatalytic activities.
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Affiliation(s)
- Nathalie Vonrüti
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
| | - Ulrich Aschauer
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
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26
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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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27
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Gazquez J, Stengel M, Mishra R, Scigaj M, Varela M, Roldan MA, Fontcuberta J, Sánchez F, Herranz G. Competition between Polar and Nonpolar Lattice Distortions in Oxide Quantum Wells: New Critical Thickness at Polar Interfaces. PHYSICAL REVIEW LETTERS 2017; 119:106102. [PMID: 28949171 DOI: 10.1103/physrevlett.119.106102] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Indexed: 05/13/2023]
Abstract
Two basic lattice distortions permeate the structural phase diagram of oxide perovskites: antiferrodistortive (AFD) rotations and tilts of the oxygen octahedral network and polar ferroelectric modes. With some notable exceptions, these two order parameters rarely coexist in a bulk crystal, and understanding their competition is a lively area of active research. Here we demonstrate, by using the LaAlO_{3}/SrTiO_{3} system as a test case, that quantum confinement can be a viable tool to shift the balance between AFD and polar modes and selectively stabilize one of the two phases. By combining scanning transmission electron microscopy (STEM) and first-principles-based models, we find a crossover between a bulklike LaAlO_{3} structure where AFD rotations prevail, to a strongly polar state with no AFD tilts at a thickness of approximately three unit cells; therefore, in addition to the celebrated electronic reconstruction, our work unveils a second critical thickness, related not to the electronic properties but to the structural ones. We discuss the implications of these findings, both for the specifics of the LaAlO_{3}/SrTiO_{3} system and for the general quest towards nanoscale control of material properties.
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Affiliation(s)
- J Gazquez
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
| | - M Stengel
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
- ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain
| | - R Mishra
- Department of Mechanical Engineering and Materials Science, Washington University in St. Louis, St. Louis, Missouri 63130, USA
| | - M Scigaj
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
| | - M Varela
- Materials Science and Technology Division, Oak Ridge National Laboratory, Tennessee 37831-6071, USA
- Departamento de Física de Materiales and Instituto Pluridisciplinar, Universidad Complutense de Madrid, Madrid 28040, Spain
| | - M A Roldan
- Departamento de Física de Materiales and Instituto Pluridisciplinar, Universidad Complutense de Madrid, Madrid 28040, Spain
| | - J Fontcuberta
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
| | - F Sánchez
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
| | - G Herranz
- Institut de Ciència de Materials de Barcelona, Campus de la UAB, 08193 Bellaterra, Spain
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28
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Interface-induced multiferroism by design in complex oxide superlattices. Proc Natl Acad Sci U S A 2017; 114:E5062-E5069. [PMID: 28607082 DOI: 10.1073/pnas.1706814114] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Interfaces between materials present unique opportunities for the discovery of intriguing quantum phenomena. Here, we explore the possibility that, in the case of superlattices, if one of the layers is made ultrathin, unexpected properties can be induced between the two bracketing interfaces. We pursue this objective by combining advanced growth and characterization techniques with theoretical calculations. Using prototype La2/3Sr1/3MnO3 (LSMO)/BaTiO3 (BTO) superlattices, we observe a structural evolution in the LSMO layers as a function of thickness. Atomic-resolution EM and spectroscopy reveal an unusual polar structure phase in ultrathin LSMO at a critical thickness caused by interfacing with the adjacent BTO layers, which is confirmed by first principles calculations. Most important is the fact that this polar phase is accompanied by reemergent ferromagnetism, making this system a potential candidate for ultrathin ferroelectrics with ferromagnetic ordering. Monte Carlo simulations illustrate the important role of spin-lattice coupling in LSMO. These results open up a conceptually intriguing recipe for developing functional ultrathin materials via interface-induced spin-lattice coupling.
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29
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Cancellieri C, Mishchenko AS, Aschauer U, Filippetti A, Faber C, Barišić OS, Rogalev VA, Schmitt T, Nagaosa N, Strocov VN. Polaronic metal state at the LaAlO3/SrTiO3 interface. Nat Commun 2016; 7:10386. [PMID: 26813124 PMCID: PMC4737810 DOI: 10.1038/ncomms10386] [Citation(s) in RCA: 112] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 12/03/2015] [Indexed: 11/16/2022] Open
Abstract
Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures.
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Affiliation(s)
- C. Cancellieri
- Swiss Light Source, Paul Scherrer Institute, Villigen CH-5232, Switzerland
- EMPA, Swiss Federal Laboratories for Materials Science & Technology, Ueberlandstrasse 129, Duebendorf 8600, Switzerland
| | - A. S. Mishchenko
- RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - U. Aschauer
- Materials Theory, ETH Zurich, Wolfgang-Pauli-Strasse 27, Zürich CH-8093, Switzerland
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3 3012 Bern, Switzerland
| | - A. Filippetti
- CNR-IOM, Istituto Officina dei Materiali, Cittadella Universitaria, Cagliari, Monserrato 09042-I, Italy
| | - C. Faber
- Materials Theory, ETH Zurich, Wolfgang-Pauli-Strasse 27, Zürich CH-8093, Switzerland
| | - O. S. Barišić
- Institute of Physics, Bijenička 46, 10000 Zagreb, Croatia
| | - V. A. Rogalev
- Swiss Light Source, Paul Scherrer Institute, Villigen CH-5232, Switzerland
| | - T. Schmitt
- Swiss Light Source, Paul Scherrer Institute, Villigen CH-5232, Switzerland
| | - N. Nagaosa
- RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - V. N. Strocov
- Swiss Light Source, Paul Scherrer Institute, Villigen CH-5232, Switzerland
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30
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Edge JM, Kedem Y, Aschauer U, Spaldin NA, Balatsky AV. Quantum Critical Origin of the Superconducting Dome in SrTiO_{3}. PHYSICAL REVIEW LETTERS 2015; 115:247002. [PMID: 26705650 DOI: 10.1103/physrevlett.115.247002] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Indexed: 06/05/2023]
Abstract
We expand the well-known notion that quantum criticality can induce superconductivity by proposing a concrete mechanism for superconductivity due to quantum ferroelectric fluctuations. To this end, we investigate the origin of superconductivity in doped SrTiO_{3} using a combination of density functional and strong coupling theories within the framework of quantum criticality. Our density functional calculations of the ferroelectric soft mode frequency as a function of doping reveal a crossover related to quantum paraelectricity at a doping level coincident with the experimentally observed top of the superconducting dome. Thus, we suggest a model in which the soft mode fluctuations provide the pairing interaction for superconductivity carriers. Within our model, the low doping limit of the superconducting dome is explained by the emergence of the Fermi surface, and the high doping limit by departure from the quantum critical regime. We predict that the highest critical temperature will increase and shift to lower carrier doping with increasing ^{18}O isotope substitution, a scenario that is experimentally verifiable. Our model is applicable to other quantum paraelectrics, such as KTaO_{3}.
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Affiliation(s)
- Jonathan M Edge
- Nordita, Center for Quantum Materials, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, 10691 Stockholm, Sweden
| | - Yaron Kedem
- Nordita, Center for Quantum Materials, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, 10691 Stockholm, Sweden
| | - Ulrich Aschauer
- Materials Theory, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zürich, Switzerland
| | - Nicola A Spaldin
- Materials Theory, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zürich, Switzerland
| | - Alexander V Balatsky
- Nordita, Center for Quantum Materials, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, 10691 Stockholm, Sweden
- Institute for Materials Science, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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