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Pascale F, Gueddida S, Doll K, Dovesi R. Band gap, Jahn-Teller deformation, octahedra rotation in transition metal perovskites LaTiO 3 . J Comput Chem 2024; 45:683-694. [PMID: 38095335 DOI: 10.1002/jcc.27274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Revised: 11/15/2023] [Accepted: 11/17/2023] [Indexed: 03/02/2024]
Abstract
The LaTiO3 perovskite (where Ti is in a d1 state) is investigated by using an all electron Gaussian basis and many functionals, ranging from pure GGA (PBE), to hybrids (full range, B3LYP and PBE0, and range separated, HSE06) to Hartree Fock. Recently, Varignon et al. (Phys. Rev. Res 1, 033131, 2019), showed that, when GGA+U or HSE06 are used, a metallic solution and fractional occupancy of the t2 g subshell are obtained. Here, it is shown that when a full range hybrid functional is used, an integer occupancy is obtained, as suggested by the Jahn-Teller theorem. When the exact exchange percentage varies from 0 to 100, the system is insulating when it exceeds 20. By reducing progressively the symmetry from cubic down to orthorhombic, the relative importance of the Jahn-Teller deformation and of the rotation of the octahedra is explored.
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Affiliation(s)
- F Pascale
- Université de Lorraine-Nancy, CNRS, LEMTA, Nancy, France
| | - S Gueddida
- Université de Lorraine-Nancy, CNRS, LPCT, UMR, Vandoeuvre-lés-Nancy, France
| | - K Doll
- University of Stuttgart, Molpro Quantum Chemistry Software, Institute of Theoretical Chemistry, Stuttgart, Germany
| | - R Dovesi
- Accademia Delle Science di Torino, Torinoto, Italy
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2
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Cao G, Weng Y, Yao X, Ward TZ, Gai Z, Mandrus D, Dong S. Effect of Mn doping and charge transfer on LaTi 1-xMn xO 3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 35:055601. [PMID: 36410040 DOI: 10.1088/1361-648x/aca4b3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2022] [Accepted: 11/21/2022] [Indexed: 06/16/2023]
Abstract
We report the magnetic and electronic transport properties of Mn-doped LaTi1-xMnxO3(x= 0, 0.1, 0.3, 0.5) as a function of temperature and an applied magnetic field. It was found that the Mn-doped samples show a magnetic transition which is not present in the parent LaTiO3. The Mn-doped samples showed fluctuations in magnetization at low fields below their Néel transition temperature indicating electronic phase separation in the material. Increased Mn content in the sample strengthens the ferromagnetic-like moment while maintaining G-type antiferromagnetic phase by charge transfer from Mn to Ti and influencing orbital ordering of the Ti3+t2gorbitals. The results are discussed in parallel with transport and bulk magnetization measurements detailing the electronic behavior. An additional context for the mechanism is supported by first-principles density-function theory calculations.
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Affiliation(s)
- Guixin Cao
- Materials Genome Institute, Shanghai University, Shanghai 200444, People's Republic of China
| | - Yakui Weng
- School of Science, Nanjing University of Posts and Telecommunications, Nanjing 210023, People's Republic of China
| | - Xinyu Yao
- Materials Genome Institute, Shanghai University, Shanghai 200444, People's Republic of China
| | - T Zac Ward
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America
| | - Zheng Gai
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37830, United States of America
| | - David Mandrus
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America
| | - Shuai Dong
- School of Physics, Southeast University, Nanjing 211189, People's Republic of China
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3
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Najev A, Hameed S, Gautreau D, Wang Z, Joe J, Požek M, Birol T, Fernandes RM, Greven M, Pelc D. Uniaxial Strain Control of Bulk Ferromagnetism in Rare-Earth Titanates. PHYSICAL REVIEW LETTERS 2022; 128:167201. [PMID: 35522519 DOI: 10.1103/physrevlett.128.167201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Revised: 10/26/2021] [Accepted: 03/04/2022] [Indexed: 06/14/2023]
Abstract
The perovskite rare-earth titanates are model Mott insulators with magnetic ground states that are very sensitive to structural distortions. These distortions couple strongly to the orbital degrees of freedom and, in principle, it should be possible to tune the superexchange and the magnetic transition with strain. We investigate the representative system (Y,La,Ca)TiO_{3}, which exhibits low crystallographic symmetry and no structural instabilities. From magnetic susceptibility measurements of the Curie temperature, we demonstrate direct, reversible, and continuous control of ferromagnetism by influencing the TiO_{6} octahedral tilts and rotations with uniaxial strain. The relative change in T_{C} as a function of strain is well described by ab initio calculations, which provides detailed understanding of the complex interactions among structural, orbital, and magnetic properties in rare-earth titanates. The demonstrated manipulation of octahedral distortions opens up far-reaching possibilities for investigations of electron-lattice coupling, competing ground states, and magnetic quantum phase transitions in a wide range of quantum materials.
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Affiliation(s)
- A Najev
- Department of Physics, Faculty of Science, University of Zagreb, Bijenička 32, HR-10000 Zagreb, Croatia
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - S Hameed
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - D Gautreau
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Z Wang
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - J Joe
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - M Požek
- Department of Physics, Faculty of Science, University of Zagreb, Bijenička 32, HR-10000 Zagreb, Croatia
| | - T Birol
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - R M Fernandes
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - M Greven
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - D Pelc
- Department of Physics, Faculty of Science, University of Zagreb, Bijenička 32, HR-10000 Zagreb, Croatia
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Wang Y, Kim M, Rehman MA, Chabungbam AS, Kim DE, Lee HS, Kymissis I, Park HH. Bipolar Resistive Switching in Lanthanum Titanium Oxide and an Increased On/Off Ratio Using an Oxygen-Deficient ZnO Interlayer. ACS APPLIED MATERIALS & INTERFACES 2022; 14:17682-17690. [PMID: 35394742 DOI: 10.1021/acsami.2c03451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The present study pioneered an oxygen migration-driven metal to insulator transition Mott memory, a new type of nonvolatile memory using lanthanum titanium oxide (LTO). We first show the reset first bipolar property without an initial electroforming process in LTO. We used oxygen-deficient ZnO as an interlayer between LTO and a W electrode to clarify whether oxygen migration activates LTO as the Mott transition. ZnO oxygen deficiency provides oxygen ion migration paths as well as a reservoir, facilitating oxygen migration from LTO to the W electrode. Thus, including the ZnO interlayer improved oxygen migration between LTO and the W electrode, achieving a 10-fold increased on/off current ratio. The current research contributes to a better understanding of valence change Mott memory by exploring the LTO resistive switching mechanism and ZnO interlayer influences on the oxygen migration process.
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Affiliation(s)
- Yue Wang
- Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Minjae Kim
- Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Malik Abdul Rehman
- Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Akendra Singh Chabungbam
- Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Dong-Eun Kim
- Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
| | - Hong Sub Lee
- Department of Materials Science and Engineering, Kangwon National University, Chuncheon 24341, Republic of Korea
| | - Ioannis Kymissis
- Department of Electrical Engineering, Columbia University, New York, New York 10027, United States
| | - Hyung-Ho Park
- Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
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5
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Synthesis, structural, optical and dielectric characterization of Y1-xSrxCuO3 nanoceramics. Chem Phys Lett 2022. [DOI: 10.1016/j.cplett.2022.139404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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6
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Sohn W, Kim TL, Lee TH, Yoon S, Kim C, Yoo JW, Roh KC, Kim M, Jang HW. Suppression of metal-to-insulator transition using strong interfacial coupling at cubic and orthorhombic perovskite oxide heterointerfaces. NANOSCALE 2021; 13:708-715. [PMID: 33367436 DOI: 10.1039/d0nr07545k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
A quasi-two-dimensional electron gas (2DEG) evolved at the LaAlO3 (LAO)/SrTiO3 (STO) interface has attracted significant attention, because the insertion of perovskite titanates can tune the 2DEG conductivity. However, this depends on the Ti-O-Ti bonding angle and structural symmetry. In this study, we controlled the octahedral tilt of the LAO/CaTiO3 (CTO) interface by heterostructuring it with CTO grown on STO substrates of various thicknesses. The 2DEG was maintained when the thickness of CTO was below the critical thickness of 5 unit cells (uc); however, it was suppressed when the CTO thickness was above the critical thickness. High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) combined with integrated differential phase contrast (iDPC) STEM imaging was used to visualize the TiO6 octahedral tilt propagation and symmetry of the 5 uc and 24 uc CTO films. The symmetry of the 5 uc CTO film resembled that of the STO substrate, whereas the octahedral tilt propagated in the 24 uc CTO film due to the structural relaxation. These results show that the interface engineering of the octahedral tilt can enable or suppress the formation of the 2DEG in perovskite oxides.
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Affiliation(s)
- Woonbae Sohn
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea and Energy Storage Materials Centre, Korea Institute of Ceramic Engineering and Technology, Jinju 52851, Republic of Korea
| | - Taemin Ludvic Kim
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Tae Hyung Lee
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Sangmoon Yoon
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Chungsoo Kim
- Technology of Analysis Centre, Korea Institute of Ceramic Engineering and Technology, Jinju 52851, Republic of Korea
| | - Jung-Woo Yoo
- School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea
| | - Kwang Chul Roh
- Energy Storage Materials Centre, Korea Institute of Ceramic Engineering and Technology, Jinju 52851, Republic of Korea
| | - Miyoung Kim
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Ho Won Jang
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
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7
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Li F, Zou Y, Han MG, Foyevtsova K, Shin H, Lee S, Liu C, Shin K, Albright SD, Sutarto R, He F, Davidson BA, Walker FJ, Ahn CH, Zhu Y, Cheng ZG, Elfimov I, Sawatzky GA, Zou K. Single-crystalline epitaxial TiO film: A metal and superconductor, similar to Ti metal. SCIENCE ADVANCES 2021; 7:7/2/eabd4248. [PMID: 33523988 PMCID: PMC7793583 DOI: 10.1126/sciadv.abd4248] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Accepted: 11/10/2020] [Indexed: 06/12/2023]
Abstract
Titanium monoxide (TiO), an important member of the rock salt 3d transition-metal monoxides, has not been studied in the stoichiometric single-crystal form. It has been challenging to prepare stoichiometric TiO due to the highly reactive Ti2+ We adapt a closely lattice-matched MgO(001) substrate and report the successful growth of single-crystalline TiO(001) film using molecular beam epitaxy. This enables a first-time study of stoichiometric TiO thin films, showing that TiO is metal but in proximity to Mott insulating state. We observe a transition to the superconducting phase below 0.5 K close to that of Ti metal. Density functional theory (DFT) and a DFT-based tight-binding model demonstrate the extreme importance of direct Ti-Ti bonding in TiO, suggesting that similar superconductivity exists in TiO and Ti metal. Our work introduces the new concept that TiO behaves more similar to its metal counterpart, distinguishing it from other 3d transition-metal monoxides.
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Affiliation(s)
- Fengmiao Li
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - Yuting Zou
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Myung-Geun Han
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Kateryna Foyevtsova
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - Hyungki Shin
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - Sangjae Lee
- Department of Physics, Yale University, New Haven, CT 06520, USA
| | - Chong Liu
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - Kidae Shin
- Department of Applied Physics, Yale University, New Haven, CT 06520, USA
| | | | - Ronny Sutarto
- Canadian Light Source, Saskatoon, Saskatchewan S7N 2V3, Canada
| | - Feizhou He
- Canadian Light Source, Saskatoon, Saskatchewan S7N 2V3, Canada
| | - Bruce A Davidson
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - Frederick J Walker
- Department of Applied Physics, Yale University, New Haven, CT 06520, USA
| | - Charles H Ahn
- Department of Physics, Yale University, New Haven, CT 06520, USA
- Department of Applied Physics, Yale University, New Haven, CT 06520, USA
| | - Yimei Zhu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Zhi Gang Cheng
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Ilya Elfimov
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - George A Sawatzky
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - Ke Zou
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
- Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
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Li Y, Zheng YS, Zhu YA, Sui ZJ, Zhou XG, Chen D, Yuan WK. BEEF-vdW+U method applied to perovskites: thermodynamic, structural, electronic, and magnetic properties. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:145901. [PMID: 30641492 DOI: 10.1088/1361-648x/aafe3e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The recently developed BEEF-vdW exchange-correlation method provides a reasonably reliable description of both long-range van der Waals interactions and short-range covalent bonding between molecules and surfaces. However, this method still suffers from the excessive electron delocalization that is connected with the self-interaction error and, consequently, the calculated chemical and physical properties such as formation energy and band gap deviate markedly from the experimental values, especially when strongly correlated systems are under investigation. In this contribution, BEEF-vdW+U calculations have been performed to study the thermodynamic, structural, electronic, and magnetic properties of La-based perovskites. An effective interaction parameter [Formula: see text] and an energy adjustment [Formula: see text] are determined simultaneously by a mixing GGA and GGA+U method, where the enthalpy or Gibbs free energy of formation of oxides containing a transition metal in different oxidation states are fitted to available experimental data. The [Formula: see text] is found to have its origin in the fact that the GGA+U method gives rise to the offsets in the total energy that include not only the desired physical correction but also an arbitrary contribution. Calculated results indicate that the BEEF-vdW method provides a more accurate description of the bonding in the O2 molecule than the PBE method and has generally smaller [Formula: see text] values for the 3d-block transition metals, thereby giving rise to band gaps and magnetic moments that are in better agreement with the experimentally measured values.
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Affiliation(s)
- Yang Li
- UNILAB, State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, People's Republic of China
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9
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Ghising P, Das D, Das S, Hossain Z. Kondo effect with tunable spin-orbit interaction in LaTiO 3/CeTiO 3/SrTiO 3 heterostructure. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:285002. [PMID: 29855435 DOI: 10.1088/1361-648x/aac977] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We have fabricated epitaxial films of CeTiO3 (CTO) on (0 0 1) oriented SrTiO3 (STO) substrates, which exhibit highly insulating and diamagnetic properties. X-ray photoelectron spectroscopy was used to establish the 3+ valence state of the Ce and Ti ions. Furthermore, we have also fabricated δ (CTO) doped LaTiO3 (LTO)/SrTiO3 thin films which exhibit variety of interesting properties including Kondo effect and spin-orbit interaction (SOI) at low temperatures. The SOI shows a non-monotonic behaviour as the thickness of the CTO layer is increased and is reflected in the value of characteristic SOI field ([Formula: see text]) obtained from weak anti-localization fitting. The maximum value of [Formula: see text] is 1.00 T for δ layer thickness of 6 u.c. This non-monotonic behaviour of SOI is attributed to the strong screening of the confining potential at the interface. The screening effect is enhanced by the CTO layer thickness and the dielectric constant of STO which increases at low temperatures. Due to the strong screening, electrons confined at the interface are spread deeper into the STO bulk where it starts to populate the Ti [Formula: see text] subbands; consequently the Fermi level crosses over from [Formula: see text] to the [Formula: see text] subbands. At the crossover region of [Formula: see text] where there is orbital mixing, SOI goes through a maximum.
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Affiliation(s)
- Pramod Ghising
- Department of Physics, Condensed Matter-Low Dimensional Systems Laboratory, Indian Institute of Technology, Kanpur-208016, India
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10
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Veit MJ, Arras R, Ramshaw BJ, Pentcheva R, Suzuki Y. Nonzero Berry phase in quantum oscillations from giant Rashba-type spin splitting in LaTiO 3/SrTiO 3 heterostructures. Nat Commun 2018; 9:1458. [PMID: 29654231 PMCID: PMC5899139 DOI: 10.1038/s41467-018-04014-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Accepted: 03/26/2018] [Indexed: 11/17/2022] Open
Abstract
The manipulation of the spin degrees of freedom in a solid has been of fundamental and technological interest recently for developing high-speed, low-power computational devices. There has been much work focused on developing highly spin-polarized materials and understanding their behavior when incorporated into so-called spintronic devices. These devices usually require spin splitting with magnetic fields. However, there is another promising strategy to achieve spin splitting using spatial symmetry breaking without the use of a magnetic field, known as Rashba-type splitting. Here we report evidence for a giant Rashba-type splitting at the interface of LaTiO3 and SrTiO3. Analysis of the magnetotransport reveals anisotropic magnetoresistance, weak anti-localization and quantum oscillation behavior consistent with a large Rashba-type splitting. It is surprising to find a large Rashba-type splitting in 3d transition metal oxide-based systems such as the LaTiO3/SrTiO3 interface, but it is promising for the development of a new kind of oxide-based spintronics. Rashba-type splitting is an effective way to manipulate the spin degrees of freedom in a solid without external magnetic field. Here, the authors demonstrate a strong Rashba-type splitting at the interface of LaTiO3 and SrTiO3 which is promising for the development of oxide-based spintronics.
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Affiliation(s)
- M J Veit
- Department of Applied Physics and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, 94305, USA.
| | - R Arras
- CEMES, University of Toulouse, CNRS, UPS, 29, rue Jeanne Marvig, 31055, Toulouse, France
| | - B J Ramshaw
- Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.,Laboratory for Atomic and Solid State Physics, Cornell University, Ithaca, NY, 14853, USA
| | - R Pentcheva
- Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, Lotharstrasse 1, 47057, Duisburg, Germany
| | - Y Suzuki
- Department of Applied Physics and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, 94305, USA
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11
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Turkowski V, Rahman TS. Nonadiabatic exchange-correlation kernel for strongly correlated materials. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:455601. [PMID: 28876226 DOI: 10.1088/1361-648x/aa8ac1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We formulate a rigorous method for calculating a nonadiabatic (frequency-dependent) exchange-correlation (XC) kernel appropriate for accurate description of both equilibrium and nonequilibrium properties of strongly correlated systems within the time-dependent density functional theory (TDDFT) via the charge susceptibility, which is in turn obtained from dynamical mean field theory (DMFT) based on the effective multi-orbital Hubbard model. Application to the simple case of the one-orbital Hubbard model already shows the importance of the nonadiabatic kernel as it leads to significant modification of the excitation spectrum-shifting the (adiabatic) peak and disclosing another that is reminiscent of the solution from DMFT. The impact of dynamical effects, naturally included through the nonadiabaticity of the XC kernel, becomes even more transparent in our consideration of the nonequilibrium charge-density response of a multi-orbital perovskite, YTiO3, to a perturbation by a femtosecond (fs) laser pulse. These initial results indicate that electron-electron correlations and nonadiabatic features may significantly affect the spectrum and nonequilibrium properties of strongly correlated systems. We also propose an algorithm for extension of the approach to non-linear response. The transparency and computational efficiency of this non-adiabatic TDDFT+DMFT approach opens the door to examination of the spectra and response of multi-orbital systems with many nonequivalent atoms-bulk material, films and nanostructures.
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Affiliation(s)
- Volodymyr Turkowski
- Department of Physics, University of Central Florida, Orlando, FL 32816, United States of America
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12
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Gu M, Rondinelli JM. Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides. Sci Rep 2016; 6:25121. [PMID: 27126354 PMCID: PMC4850389 DOI: 10.1038/srep25121] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2016] [Accepted: 04/11/2016] [Indexed: 11/28/2022] Open
Abstract
We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.
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Affiliation(s)
- Mingqiang Gu
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA
| | - James M. Rondinelli
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA
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13
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Engineered Mott ground state in a LaTiO(3+δ)/LaNiO3 heterostructure. Nat Commun 2016; 7:10418. [PMID: 26791402 PMCID: PMC4735946 DOI: 10.1038/ncomms10418] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Accepted: 12/09/2015] [Indexed: 11/08/2022] Open
Abstract
In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO3 and a doped Mott insulator LaTiO3+δ, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and eg orbital band splitting. Our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states. Interfaces between two dissimilar transition metal oxides can exhibit emergent strongly correlated electronic and magnetic states due to charge transfer and electronic reconfiguration. Here, the authors synthesize and investigate an exotic Mott ground state in LaTiO3+δ/LaNiO3 heterostructures.
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Ulrich C, Khaliullin G, Guennou M, Roth H, Lorenz T, Keimer B. Spin-Orbital Excitation Continuum and Anomalous Electron-Phonon Interaction in the Mott Insulator LaTiO_{3}. PHYSICAL REVIEW LETTERS 2015; 115:156403. [PMID: 26550738 DOI: 10.1103/physrevlett.115.156403] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Indexed: 06/05/2023]
Abstract
Raman scattering experiments on stoichiometric, Mott-insulating LaTiO_{3} over a wide range of excitation energies reveal a broad electronic continuum which is featureless in the paramagnetic state, but develops a gap of ~800 cm^{-1} upon cooling below the Néel temperature T_{N}=146 K. In the antiferromagnetic state, the spectral weight below the gap is transferred to well-defined spectral features due to spin and orbital excitations. Low-energy phonons exhibit pronounced Fano anomalies indicative of strong interaction with the electron system for T>T_{N}, but become sharp and symmetric for T<T_{N}. The electronic continuum and the marked renormalization of the phonon lifetime by the onset of magnetic order are highly unusual for Mott insulators and indicate liquidlike correlations between spins and orbitals.
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Affiliation(s)
- C Ulrich
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany
| | - G Khaliullin
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany
| | - M Guennou
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany
- Materials Research and Technology Department, Luxembourg Institute of Science and Technology, 41 rue du Brill, L-4422 Belvaux, Luxembourg
| | - H Roth
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
| | - T Lorenz
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
| | - B Keimer
- Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany
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Goodenough JB, Zhou J. Varied roles of Pb in transition-metal Pb MO 3 perovskites ( M = Ti, V, Cr, Mn, Fe, Ni, Ru). SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 2015; 16:036003. [PMID: 27877814 PMCID: PMC5099851 DOI: 10.1088/1468-6996/16/3/036003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Revised: 02/26/2015] [Accepted: 02/26/2015] [Indexed: 05/09/2023]
Abstract
Different structural chemistries resulting from the Pb2+ lone-pair electrons in the PbMO3 perovskites are reviewed. The Pb2+ lone-pair electrons enhance the ferroelectric transition temperature in PbTiO3, stabilize vanadyl formation in PbVO3, and induce a disproportionation reaction of CrIV in PbCrO3. A Pb2+ + NiIV = Pb4+ + NiII reaction in PbNiO3 stabilizes the LiNbO3 structure at ambient pressure, but an A-site Pb4+ in an orthorhombic perovskite PbNiO3 is stabilized at modest pressures at room temperature. In PbMnO3, a ferroelectric displacement due to the lone pair electron effect is minimized by the spin-spin exchange interaction and the strong octahedral site preference of the MnIV/III cation. PbRuO3 is converted under pressure from the defective pyrochlore to the orthorhombic (Pbnm) perovskite structure where Pb-Ru interactions via a common O -2p orbital stabilize at low temperature a metallic Imma phase at ambient pressure. Above Pc [Formula: see text] a covalent Pb-Ru bond is formed by Pb2+ + RuIV = Pb4+ + RuII electron sharing.
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Affiliation(s)
| | - Jianshi Zhou
- Materials Science and Engineering Program and Texas Materials Institute, University of Texas at Austin, Austin, TX 78712, USA
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16
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Ferromagnetism induced by entangled charge and orbital orderings in ferroelectric titanate perovskites. Nat Commun 2015; 6:6677. [PMID: 25807180 PMCID: PMC4389245 DOI: 10.1038/ncomms7677] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 02/18/2015] [Indexed: 11/08/2022] Open
Abstract
In magnetic materials, the Pauli exclusion principle typically drives anti-alignment between electron spins on neighbouring species resulting in antiferromagnetic behaviour. Ferromagnetism exhibiting spontaneous spin alignment is a fairly rare behaviour, but once materialized is often associated with itinerant electrons in metals. Here we predict and rationalize robust ferromagnetism in an insulating oxide perovskite structure based on the popular titanate series. In half-doped layered titanates, the combination of Jahn–Teller and oxygen breathing motions opens a band gap and creates an unusual charge and orbital ordering of the Ti d electrons. It is argued that this intriguingly intricate electronic network favours the elusive inter-site ferromagnetic (FM) ordering, on the basis of intra-site Hund's rules. Finally, we find that the layered oxides are also ferroelectric with a spontaneous polarization approaching that of BaTiO3. The concepts are general and design principles of the technologically desirable FM ferroelectric multiferroics are presented. Magnetic insulators often display antiferromagnetic ordering owing to implications from the Pauli exclusion principle. Here, the authors predict ferromagnetism on the basis of intra-site Hund's rules in ferroelectric titanate superlattices showing charge and Jahn–Teller induced orbital orderings.
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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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SrTiO 3 -based perovskites: Preparation, characterization and photocatalytic activity in gas–solid regime under simulated solar irradiation. J Catal 2015. [DOI: 10.1016/j.jcat.2014.10.014] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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19
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Bernardo P, Ghivelder L, Eslava G, Amorim H, Felner I, Garcia S. Monoclinic distortion and magnetic coupling in the double perovskite Sr 2−x Ca x YRuO 6. J SOLID STATE CHEM 2014. [DOI: 10.1016/j.jssc.2014.09.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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21
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Jang HW, Felker DA, Bark CW, Wang Y, Niranjan MK, Nelson CT, Zhang Y, Su D, Folkman CM, Baek SH, Lee S, Janicka K, Zhu Y, Pan XQ, Fong DD, Tsymbal EY, Rzchowski MS, Eom CB. Metallic and Insulating Oxide Interfaces Controlled by Electronic Correlations. Science 2011; 331:886-9. [DOI: 10.1126/science.1198781] [Citation(s) in RCA: 193] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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22
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Jang SY, Kim H, Moon SJ, Choi WS, Jeon BC, Yu J, Noh TW. The electronic structure of epitaxially stabilized 5d perovskite Ca(1-x)Sr(x)IrO3 (x = 0, 0.5, and 1) thin films: the role of strong spin-orbit coupling. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:485602. [PMID: 21406751 DOI: 10.1088/0953-8984/22/48/485602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We have investigated the electronic structure of meta-stable perovskite Ca(1 - x)Sr(x)IrO(3)(x = 0, 0.5, and 1) thin films using transport measurements, optical spectroscopy, and first-principles calculations. We artificially fabricated the perovskite phase of Ca(1 - x)Sr(x)IrO(3), which has a hexagonal or post-perovskite crystal structure in bulk form, by growing epitaxial thin films on perovskite GdScO(3) substrates using an epi-stabilization technique. The transport properties of the perovskite Ca(1 - x)Sr(x)IrO(3) films systematically change from nearly insulating (or semi-metallic) for x = 0 to weakly metallic for x = 1. Due to the extended wavefunctions, 5d electrons are usually delocalized. However, the strong spin-orbit coupling in Ca(1 - x)Sr(x)IrO(3) results in the formation of effective total angular momentum J(eff) = 1/2 and 3/2 states, which puts Ca(1 - x)Sr(x)IrO(3) in the vicinity of a metal-insulator phase boundary. As a result, the electrical properties of the Ca(1 - x)Sr(x)IrO(3) films are found to be sensitive to x and strain.
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Affiliation(s)
- S Y Jang
- ReCFI, Department of Physics and Astronomy, Seoul National University, Seoul, Republic of Korea
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23
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Seo SSA, Han MJ, Hassink GWJ, Choi WS, Moon SJ, Kim JS, Susaki T, Lee YS, Yu J, Bernhard C, Hwang HY, Rijnders G, Blank DHA, Keimer B, Noh TW. Two-dimensional confinement of 3d{1} electrons in LaTiO_{3}/LaAlO{3} multilayers. PHYSICAL REVIEW LETTERS 2010; 104:036401. [PMID: 20366664 DOI: 10.1103/physrevlett.104.036401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2009] [Indexed: 05/29/2023]
Abstract
We report spectroscopic ellipsometry measurements of the anisotropy of the interband transitions parallel and perpendicular to the planes of (LaTiO3)n(LaAlO3)5 multilayers with n=1-3. These provide direct information about the electronic structure of the two-dimensional (2D) 3d{1} state of the Ti ions. In combination with local density approximation, including a Hubbard U calculation, we suggest that 2D confinement in the TiO2 slabs lifts the degeneracy of the t{2g} states leaving only the planar d{xy} orbitals occupied. We outline that these multilayers can serve as a model system for the study of the t{2g} 2D Hubbard model.
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Affiliation(s)
- S S A Seo
- Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea.
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24
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Uchida M, Fujioka J, Onose Y, Tokura Y. Charge dynamics in thermally and doping induced insulator-metal transitions of (Ti1-xVx)2O3. PHYSICAL REVIEW LETTERS 2008; 101:066406. [PMID: 18764483 DOI: 10.1103/physrevlett.101.066406] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2008] [Indexed: 05/26/2023]
Abstract
Charge dynamics of (Ti1-xVx)2O3 with x=0-0.06 has been investigated by measurements of charge transport and optical conductivity spectra in a wide temperature range of 2-600 K with the focus on the thermally and doping induced insulator-metal transitions (IMTs). The optical conductivity peaks for the interband transitions in the 3d t_{2g} manifold are observed in both the insulating and metallic states, while their large variation (by approximately 0.4 eV) with change of temperature and doping level scales with that of the Ti-Ti dimer bond length, indicating the weakened singlet bond in the course of IMTs. The thermally and V-doping induced IMTs are driven with the increase in carrier density by band crossing and hold doping, respectively, in contrast with the canonical IMT of correlated oxides accompanied by the whole collapse of the Mott gap.
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Affiliation(s)
- M Uchida
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
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25
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Kitagawa J, Kadoya Y, Tsubota M, Iga F, Takabatake T. Terahertz conductivity of localized photoinduced carriers in a Mott insulator YTiO(3) at low excitation density, contrasted with the metallic nature in a band semiconductor Si. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2007; 19:406224. [PMID: 22049122 DOI: 10.1088/0953-8984/19/40/406224] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We performed optical-pump terahertz-probe measurements of a Mott insulator YTiO(3) and a band semiconductor Si using a laser diode (1.47 eV) and a femtosecond-pulse laser (1.55 eV). Both samples possess long energy-relaxation times (1.5 ms for YTiO(3) and 15 µs for Si); therefore, it is possible to extract terahertz complex conductivities of photoinduced carriers under equilibrium. We observed highly contrasting behaviour-Drude conductivity in Si and localized conductivity possibly obeying the Jonscher law in YTiO(3). The carrier number at the highest carrier-concentration layer in YTiO(3) is estimated to be 0.015 per Ti site. Anisotropic conductivity of YTiO(3) is determined. Our study indicates that localized carriers might play an important role in the incipient formation of photoinduced metallic phases in Mott insulators. In addition, this study shows that the transfer-matrix method is effective for extracting an optical constant of a sample with a spatially inhomogeneous carrier distribution.
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Affiliation(s)
- J Kitagawa
- Department of Quantum Matter, ADSM, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8530, Japan
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26
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Loa I, Wang X, Syassen K, Roth H, Lorenz T, Hanfland M, Mathis YL. Crystal structure and the Mott-Hubbard gap in YTiO(3) at high pressure. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2007; 19:406223. [PMID: 22049150 DOI: 10.1088/0953-8984/19/40/406223] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The crystal structure of YTiO(3) at high pressures up to 30 GPa has been investigated by means of synchrotron x-ray powder diffraction (T = 295 K). The variation of the Ti-O bond lengths with pressure evidences a distinct change in the distortion of the TiO(6) octahedra at around 10 GPa, which is discussed in terms of a pressure-driven spatial reorientation of the occupied Ti 3d(t(2g)) orbitals. Mid-infrared synchrotron microspectroscopy has been used to determine quantitatively the pressure-induced reduction of the optical bandgap of YTiO(3), and the results are interpreted on the basis of the structural and possible orbital orientation changes.
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Affiliation(s)
- I Loa
- Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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27
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De Raychaudhury M, Pavarini E, Andersen OK. Orbital fluctuations in the different phases of LaVO(3) and YVO(3). PHYSICAL REVIEW LETTERS 2007; 99:126402. [PMID: 17930528 DOI: 10.1103/physrevlett.99.126402] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2007] [Indexed: 05/25/2023]
Abstract
We investigate the importance of quantum orbital fluctuations in the orthorhombic and monoclinic phases of the Mott insulators LaVO(3) and YVO(3). First, we construct ab initio material-specific t(2g) Hubbard models. Then, by using dynamical mean-field theory, we calculate the spectral matrix as a function of temperature. Our Hubbard bands and Mott gaps are in very good agreement with spectroscopy. We show that in orthorhombic LaVO(3), quantum orbital fluctuations are strong and that they are suppressed only in the monoclinic 140 K phase. In YVO(3)the suppression happens already at 300 K. We show that Jahn-Teller and GdFeO3-type distortions are both crucial in determining the type of orbital and magnetic order in the low temperature phases.
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Affiliation(s)
- M De Raychaudhury
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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28
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Ulrich C, Gössling A, Grüninger M, Guennou M, Roth H, Cwik M, Lorenz T, Khaliullin G, Keimer B. Raman scattering in the Mott insulators LaTiO3 and YTiO3: evidence for orbital excitations. PHYSICAL REVIEW LETTERS 2006; 97:157401. [PMID: 17155355 DOI: 10.1103/physrevlett.97.157401] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2005] [Indexed: 05/12/2023]
Abstract
Raman scattering is used to observe pronounced electronic excitations around 230 meV--well above the two-phonon range--in the Mott insulators LaTiO3 and YTiO3. Based on the temperature, polarization, and photon energy dependence, the modes are identified as orbital excitations. The observed profiles bear a striking resemblance to magnetic Raman modes in the insulating parent compounds of the superconducting cuprates, indicating an unanticipated universality of the electronic excitations in transition metal oxides.
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Affiliation(s)
- C Ulrich
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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Wang FB, Li J, Wang P, Zhu XH, Zhang MJ, Peng ZH, Li SL, Yong LP, Chen YF, Sun XS, Zheng DN. Effect of oxygen content on the transport properties of LaTiO(3+β/2) thin films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2006; 18:5835-5847. [PMID: 21690800 DOI: 10.1088/0953-8984/18/26/004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The structural and transport properties of LaTiO(3+β/2) epitaxial thin films, grown at different oxygen pressures ranging from 6.6 × 10(-4) to 5 Pa, have been investigated. X-ray diffraction peaks of the films shift to lower angles with increasing oxygen pressure, indicative of a variation of the corresponding lattice spacing. All the films show T(2) dependence of resistivity over a large temperature range of ∼200 K, suggesting a band-filling-induced metallic Fermi-liquid behaviour. Upturns in resistivity have been revealed at low temperatures, which could be ascribed to the Anderson-localization effect caused by the cation vacancies. Furthermore, for the thin films grown at high oxygen pressures of 0.5 and 5 Pa, the dependence of resistivity on temperature shows a maximum at high temperatures. The maximum seems to support the argument that transition between t-orbital ordering and disordering plays an important role in dominating transport properties at high temperatures. Carrier density deduced from Hall coefficient increases with the decrease of oxygen content, and shows strong temperature dependence. From the experimental data, it can be asserted that in the LaTiO(3+β/2) thin films, besides the band filling effect, localization or disorder caused by La and Ti vacancy effects controls the unique transport properties.
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Affiliation(s)
- F B Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China. Department of Materials Science, Sichuan University, Chengdu 610064, People's Republic of China
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31
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Nakayama M, Usui T, Uchimoto Y, Wakihara M, Yamamoto M. Changes in Electronic Structure upon Lithium Insertion into the A-Site Deficient Perovskite Type Oxides (Li,La)TiO3. J Phys Chem B 2005; 109:4135-43. [PMID: 16851474 DOI: 10.1021/jp046062j] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Investigation on variation of the electronic structure accompanying the electrochemical lithium insertion into the perovskite type oxide, (Li,La)TiO3, has been carried out by X-ray absorption spectroscopy (XAS). During the electrochemical lithium insertion, titanium ion reduced its oxidation state from Ti4+ to Ti3+, while La3+ does not contribute to the reduction reaction resulting from Ti K-edge and La L3-edge XAS, respectively. Furthermore, O K-edge XAS showed marked spectral changes with electrochemical lithium insertion, indicating the electronic structure around oxide ion affected by lithium insertion reaction. From the XAS measurement, we have concluded the variation observed in O K-edge XAS was related to the strong interaction with inserted Li ion. To confirm this, first-principles band calculations were performed for the perovskite structure before and after electrochemical lithium insertion. The calculated results showed that the electron originated from inserted Li transferred to neighboring oxide ion locally as well as to Ti ion. This may be due to local neutralization effect of Li to reduce the electrostatic interaction in the crystal.
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Affiliation(s)
- Masanobu Nakayama
- Department of Applied Chemistry, Tokyo Institute of Technology, Ookayama, Tokyo 152-8552, Japan
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32
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Iga F, Tsubota M, Sawada M, Huang HB, Kura S, Takemura M, Yaji K, Nagira M, Kimura A, Jo T, Takabatake T, Namatame H, Taniguchi M. Determination of the orbital polarization in YTiO3 by using soft X-ray linear dichroism. PHYSICAL REVIEW LETTERS 2004; 93:257207. [PMID: 15697937 DOI: 10.1103/physrevlett.93.257207] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2004] [Indexed: 05/24/2023]
Abstract
We report measurements of linear dichroism in x-ray absorption at Ti L(2,3) edges of a Mott-insulating ferromagnet YTiO3, where orbital ordering occurs in the triply degenerate Ti 3d t(2g) states. Dichroic spectra and their integrated intensities are obtained for the incident electric field with polarizations parallel to a, b, and c axes. The comparison of the spectra with atomic multiplet calculations removes the ambiguity about the orbital polarization, i.e., the relative weights of |xy>, |yz>, and |zx> orbits, which are crucial for the origin of ferromagnetism. The result is consistent with the previous analysis of nuclear magnetic resonance in the Mizokawa-Fujimori scheme.
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Affiliation(s)
- F Iga
- Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima, 739-8530, Japan
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33
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Fang Z, Nagaosa N. Quantum versus Jahn-Teller orbital physics in YVO3 and LaVO3. PHYSICAL REVIEW LETTERS 2004; 93:176404. [PMID: 15525096 DOI: 10.1103/physrevlett.93.176404] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2004] [Indexed: 05/24/2023]
Abstract
We argue that the large Jahn-Teller (JT) distortions in YVO3 and LaVO3 should suppress the quantum orbital fluctuation. The unusual magnetic properties can be well explained based on local density approximation + Hubbard U calculations using experimental structures, in terms of the JT orbital. The observed splitting of the spin-wave dispersions for YVO3 in a C-type antiferromagnetic state is attributed to the inequivalent VO2 layers in the crystal structure, instead of the "orbital-Peierls state." Alternative stacking of ab-plane exchange couplings produces the c-axis spin-wave splitting; thus, the spin system is highly three dimensional rather than quasi-one-dimensional. Similar splitting is also predicted for LaVO3, although it is weak.
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Affiliation(s)
- Zhong Fang
- Institute of Physics, Chinese Academy of Science, Beijing 100080, China
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Pavarini E, Biermann S, Poteryaev A, Lichtenstein AI, Georges A, Andersen OK. Mott transition and suppression of orbital fluctuations in orthorhombic 3d1 perovskites. PHYSICAL REVIEW LETTERS 2004; 92:176403. [PMID: 15169176 DOI: 10.1103/physrevlett.92.176403] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2003] [Indexed: 05/13/2023]
Abstract
Using t(2g) Wannier functions, a low-energy Hamiltonian is derived for orthorhombic 3d(1) transition-metal oxides. Electronic correlations are treated with a new implementation of dynamical mean-field theory for noncubic systems. Good agreement with photoemission data is obtained. The interplay of correlation effects and cation covalency (GdFeO3-type distortions) is found to suppress orbital fluctuations in LaTiO3 and even more in YTiO3, and to favor the transition to the insulating state.
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Affiliation(s)
- E Pavarini
- INFM and Dipartimento di Fisica A. Volta, Università di Pavia, Via Bassi 6, I-27100 Pavia, Italy
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Okamoto S, Millis AJ. Electronic reconstruction at an interface between a Mott insulator and a band insulator. Nature 2004; 428:630-3. [PMID: 15071589 DOI: 10.1038/nature02450] [Citation(s) in RCA: 453] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2003] [Accepted: 03/01/2004] [Indexed: 11/09/2022]
Abstract
Surface science is an important and well-established branch of materials science involving the study of changes in material properties near a surface or interface. A fundamental issue has been atomic reconstruction: how the surface lattice symmetry differs from the bulk. 'Correlated-electron compounds' are materials in which strong electron-electron and electron-lattice interactions produce new electronic phases, including interaction-induced (Mott) insulators, many forms of spin, charge and orbital ordering, and (presumably) high-transition-temperature superconductivity. Here we propose that the fundamental issue for the new field of correlated-electron surface/interface science is 'electronic reconstruction': how does the surface/interface electronic phase differ from that in the bulk? As a step towards a general understanding of such phenomena, we present a theoretical study of an interface between a strongly correlated Mott insulator and a band insulator. We find dramatic interface-induced electronic reconstructions: in wide parameter ranges, the near-interface region is metallic and ferromagnetic, whereas the bulk phase on either side is insulating and antiferromagnetic. Extending the analysis to a wider range of interfaces and surfaces is a fundamental scientific challenge and may lead to new applications for correlated electron materials.
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Affiliation(s)
- Satoshi Okamoto
- Department of Physics, Columbia University 538 West 120th Street, New York, New York 10027, USA
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Hemberger J, Krug von Nidda HA, Fritsch V, Deisenhofer J, Lobina S, Rudolf T, Lunkenheimer P, Lichtenberg F, Loidl A, Bruns D, Büchner B. Evidence for Jahn-Teller distortions at the antiferromagnetic transition in LaTiO3. PHYSICAL REVIEW LETTERS 2003; 91:066403. [PMID: 12935091 DOI: 10.1103/physrevlett.91.066403] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2003] [Indexed: 05/24/2023]
Abstract
LaTiO3 is known as a Mott insulator which orders antiferromagnetically at T(N)=146 K. We report on results of thermal expansion and temperature dependent x-ray diffraction together with measurements of the heat capacity, electrical transport measurements, and optical spectroscopy in untwinned single crystals. At T(N) significant structural changes appear, which are volume conserving. Concomitant anomalies are also observed in the dc resistivity, in bulk modulus, and optical reflectivity spectra. We interpret these experimental observations as evidence of orbital order.
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Affiliation(s)
- J Hemberger
- EKM, Institut für Physik, Universität Augsburg, D-86135 Augsburg, Germany
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Ulrich C, Khaliullin G, Okamoto S, Reehuis M, Ivanov A, He H, Taguchi Y, Tokura Y, Keimer B. Magnetic order and dynamics in an orbitally degenerate ferromagnetic insulator. PHYSICAL REVIEW LETTERS 2002; 89:167202. [PMID: 12398750 DOI: 10.1103/physrevlett.89.167202] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2002] [Indexed: 05/21/2023]
Abstract
Neutron scattering was used to determine the spin structure and the magnon spectrum of the Mott-Hubbard insulator YTiO3. The magnetic structure is complex, comprising substantial G-type and A-type antiferromagnetic components in addition to the predominant ferromagnetic component. The magnon spectrum, on the other hand, is gapless and nearly isotropic. We show that these findings are inconsistent with the orbitally ordered states thus far proposed for YTiO3 and discuss general implications for a theoretical description of exchange interactions in orbitally degenerate systems.
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Affiliation(s)
- C Ulrich
- Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart, Germany
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Optical Spectroscopic Studies of Metal-Insulator Transitions in Perovskite-Related Oxides. STRUCTURE AND BONDING 2001. [DOI: 10.1007/3-540-45503-5_4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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Meta–Insulator Phenomena in Strongly Correlated Oxides. The Vacancy-Doped Titanate Perovksites, Nd1−xTiO3 and Sm1−xTiO3. J SOLID STATE CHEM 2000. [DOI: 10.1006/jssc.2000.8932] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Yamaguchi S, Okimoto Y, Tokura Y. Bandwidth dependence of insulator-metal transitions in perovskite cobalt oxides. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 54:R11022-R11025. [PMID: 9984976 DOI: 10.1103/physrevb.54.r11022] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Mizokawa T, Fujimori A. Electronic structure and orbital ordering in perovskite-type 3d transition-metal oxides studied by Hartree-Fock band-structure calculations. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 54:5368-5380. [PMID: 9986496 DOI: 10.1103/physrevb.54.5368] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Kajueter H, Kotliar G. New Iterative Perturbation Scheme for Lattice Models with Arbitrary Filling. PHYSICAL REVIEW LETTERS 1996; 77:131-134. [PMID: 10061789 DOI: 10.1103/physrevlett.77.131] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Kajueter H, Kotliar G, Moeller G. Doped Mott insulator: Results from mean-field theory. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 53:16214-16226. [PMID: 9983454 DOI: 10.1103/physrevb.53.16214] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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45
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Katsufuji T, Okimoto Y, Tokura Y. Spectral weight transfer of the optical conductivity in doped Mott insulators. PHYSICAL REVIEW LETTERS 1995; 75:3497-3500. [PMID: 10059601 DOI: 10.1103/physrevlett.75.3497] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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