1
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Roy AP, Ss J, Dwij V, Khandelwal A, Chattopadhyay MK, Sathe V, Mittal R, Sastry PU, Achary SN, Tyagi AK, Babu PD, Le MD, Bansal D. Evidence of Strong Orbital-Selective Spin-Orbital-Phonon Coupling in CrVO_{4}. PHYSICAL REVIEW LETTERS 2024; 132:026701. [PMID: 38277598 DOI: 10.1103/physrevlett.132.026701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Revised: 12/05/2023] [Accepted: 12/14/2023] [Indexed: 01/28/2024]
Abstract
Coupling of orbital degree of freedom with a spin exchange, i.e., Kugel-Khomskii-type interaction (KK), governs a host of material properties, including colossal magnetoresistance, enhanced magnetoelectric response, and photoinduced high-temperature magnetism. In general, KK-type interactions lead to deviation in experimental observables of coupled Hamiltonian near or below the magnetic transition. Using diffraction and spectroscopy experiments, here we report anomalous changes in lattice parameters, electronic states, spin dynamics, and phonons at four times the Néel transition temperature (T_{N}) in CrVO_{4}. The temperature is significantly higher than other d-orbital compounds such as manganites and vanadates, where effects are limited to near or below T_{N}. The experimental observations are rationalized using first-principles and Green's function-based phonon and spin simulations that show unprecedentedly strong KK-type interactions via a superexchange process and an orbital-selective spin-phonon coupling coefficient at least double the magnitude previously reported for strongly coupled spin-phonon systems. Our results present an opportunity to explore the effect of KK-type interactions and spin-phonon coupling well above T_{N} and possibly bring various properties closer to application, for example, strong room-temperature magnetoelectric coupling.
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Affiliation(s)
- Aditya Prasad Roy
- Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra 400076, India
| | - Jayakrishnan Ss
- Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra 400076, India
| | - Vivek Dwij
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai, Maharashtra 400076, India
| | - Ashish Khandelwal
- Free Electron Laser Utilization Laboratory, Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013, India
| | - M K Chattopadhyay
- Free Electron Laser Utilization Laboratory, Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013, India
- Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094, India
| | - Vasant Sathe
- UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore, Madhya Pradesh 452001, India
| | - Ranjan Mittal
- Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094, India
- Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085, India
| | - P U Sastry
- Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094, India
- Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085, India
| | - Srungarpu N Achary
- Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094, India
- Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - Avesh K Tyagi
- Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094, India
- Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - Peram D Babu
- UGC-DAE Consortium for Scientific Research, Mumbai Centre, R5-Shed, BARC, Trombay, Mumbai, Maharashtra 400085, India
| | - Manh Duc Le
- ISIS facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX Oxfordshire, United Kingdom
| | - Dipanshu Bansal
- Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra 400076, India
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2
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Wang L, He W, Huang G, Xue H, Zhang G, Mu G, Wu S, An Z, Zheng C, Chen Y, Li W. Two-Dimensional Superconductivity at the Titanium Sesquioxide Heterointerface. ACS NANO 2022; 16:16150-16157. [PMID: 36121352 DOI: 10.1021/acsnano.2c04795] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The study of exotic superconductivity in two dimensions has been a central theme in the solid state and materials research communities. Experimentally exploring and identifying exotic, fascinating interface superconductors with a high transition temperature (Tc) are challenging. Here, we report an experimental observation of intriguing two-dimensional superconductivity with a Tc of up to 3.8 K at the interface between a Mott insulator Ti2O3 and polar semiconductor GaN. At the verge of superconductivity, we also observe a striking quantum metallic-like state, demonstrating that it is a precursor to the two-dimensional superconductivity as the temperature is decreased. Our work shows an exciting opportunity to exploit the underlying, emergent quantum phenomena at the heterointerfaces via heterostructure engineering.
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Affiliation(s)
- Lijie Wang
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Wenhao He
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Guangyi Huang
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Huanyi Xue
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Guanqun Zhang
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Gang Mu
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Shiwei Wu
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
- Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai 200433, China
| | - Zhenghua An
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
- Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai 200433, China
| | - Changlin Zheng
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Yan Chen
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Wei Li
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
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3
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Kim YJ, Lee C, Park HS, Yeo Y, Safarina GA, Le DD, Kim JG, Bang D, Cho BG, Park JH, Ko KT, Koo TY, Shim JH, Yang CH. Orbital Order Melting at Reduced Dimensions. NANO LETTERS 2022; 22:1059-1066. [PMID: 35084865 DOI: 10.1021/acs.nanolett.1c04117] [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 orbital degree of freedom, strongly coupled with the lattice and spin, is an important factor when designing correlated functions. Whether the long-range orbital order is stable at reduced dimensions and, if not, what the critical thickness is remains a tantalizing question. Here, we report the melting of orbital ordering, observed by controlling the dimensionality of the canonical eg1 orbital system LaMnO3. Epitaxial films are synthesized with vertically aligned orbital ordering planes on an orthorhombic substrate, so that reducing film thickness changes the two-dimensional planes into quasi-one-dimensional nanostrips. The orbital order appears to be suppressed below the critical thickness of about six unit cells by changing the characteristic phonon modes and making the Mn d orbital more isotropic. Density functional calculations reveal that the electronic energy instability induced by bandwidth narrowing via the dimensional crossover and the interfacial effect causes the absence of orbital order in the ultrathin thickness.
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Affiliation(s)
- Yong-Jin Kim
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, Daejeon 34141, Republic of Korea
- Center for Lattice Defectronics, KAIST, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Changhoon Lee
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
- Department of Physics, POSTECH, Pohang 37673, Republic of Korea
- MPPHC-CPM, Max Planck POSTECH/Korea Research Initiative (MPK), Pohang 37673, Republic of Korea
| | - Heung-Sik Park
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, Daejeon 34141, Republic of Korea
- Center for Lattice Defectronics, KAIST, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Youngki Yeo
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, Daejeon 34141, Republic of Korea
- Center for Lattice Defectronics, KAIST, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Giovanni Annur Safarina
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, Daejeon 34141, Republic of Korea
- Center for Lattice Defectronics, KAIST, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Duc Duy Le
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, Daejeon 34141, Republic of Korea
- Center for Lattice Defectronics, KAIST, Yuseong-gu, Daejeon 34141, Republic of Korea
| | - Jeong-Gyu Kim
- Department of Physics, POSTECH, Pohang 37673, Republic of Korea
- MPPHC-CPM, Max Planck POSTECH/Korea Research Initiative (MPK), Pohang 37673, Republic of Korea
| | - Daehyeon Bang
- Department of Physics, POSTECH, Pohang 37673, Republic of Korea
- MPPHC-CPM, Max Planck POSTECH/Korea Research Initiative (MPK), Pohang 37673, Republic of Korea
| | - Byeong-Gwan Cho
- Pohang Accelerator Laboratory, POSTECH, Pohang 37673, Republic of Korea
| | - Jae-Hoon Park
- Department of Physics, POSTECH, Pohang 37673, Republic of Korea
- MPPHC-CPM, Max Planck POSTECH/Korea Research Initiative (MPK), Pohang 37673, Republic of Korea
| | - Kyung-Tae Ko
- MPPHC-CPM, Max Planck POSTECH/Korea Research Initiative (MPK), Pohang 37673, Republic of Korea
- Korea Basic Science Institute, Daejeon 34133, Republic of Korea
| | - Tae Yeong Koo
- Pohang Accelerator Laboratory, POSTECH, Pohang 37673, Republic of Korea
| | - Ji Hoon Shim
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
| | - Chan-Ho Yang
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, Daejeon 34141, Republic of Korea
- Center for Lattice Defectronics, KAIST, Yuseong-gu, Daejeon 34141, Republic of Korea
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4
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Stepanov EA, Nomura Y, Lichtenstein AI, Biermann S. Orbital Isotropy of Magnetic Fluctuations in Correlated Electron Materials Induced by Hund's Exchange Coupling. PHYSICAL REVIEW LETTERS 2021; 127:207205. [PMID: 34860069 DOI: 10.1103/physrevlett.127.207205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 06/16/2021] [Accepted: 10/01/2021] [Indexed: 06/13/2023]
Abstract
Characterizing nonlocal magnetic fluctuations in materials with strong electronic Coulomb interactions remains one of the major outstanding challenges of modern condensed matter theory. In this Letter, we address the spatial symmetry and orbital structure of magnetic fluctuations in perovskite materials. To this aim, we develop a consistent multiorbital diagrammatic extension of dynamical mean-field theory, which we apply to an anisotropic three-orbital model of cubic t_{2g} symmetry. We find that the form of spatial spin fluctuations is governed by the local Hund's coupling. For small values of the coupling, magnetic fluctuations are anisotropic in orbital space, which reflects the symmetry of the considered t_{2g} model. Large Hund's coupling enhances collective spin excitations, which mixes orbital and spatial degrees of freedom, and magnetic fluctuations become orbitally isotropic. Remarkably, this effect can be seen only in two-particle quantities; single-particle observables remain anisotropic for any value of the Hund's coupling. Importantly, we find that the orbital isotropy can be induced both at half filling and for the case of four electrons per lattice site, where the magnetic instability is associated with different, antiferromagnetic and ferromagnetic, modes, respectively.
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Affiliation(s)
- Evgeny A Stepanov
- I. Institute of Theoretical Physics, University of Hamburg, Jungiusstrasse 9, 20355 Hamburg, Germany
- Theoretical Physics and Applied Mathematics Department, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
| | - Yusuke Nomura
- RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Alexander I Lichtenstein
- I. Institute of Theoretical Physics, University of Hamburg, Jungiusstrasse 9, 20355 Hamburg, Germany
- Theoretical Physics and Applied Mathematics Department, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
| | - Silke Biermann
- CPHT, CNRS, Ecole Polytechnique, Institut Polytechnique de Paris, F-91128 Palaiseau, France
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
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5
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Mattsson S, Paulus B. Density Functional Theory Calculations of Structural, Electronic, and Magnetic Properties of the 3d Metal Trifluorides MF 3 (M = Ti-Ni) in the Solid State. J Comput Chem 2019; 40:1190-1197. [PMID: 30697774 DOI: 10.1002/jcc.25777] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Revised: 12/19/2018] [Accepted: 12/22/2018] [Indexed: 11/05/2022]
Abstract
We employ density functional theory with Hubbard U correction or hybrid functionals to study the series of magnetic 3d metal trifluorides MF3 (M = Ti-Ni). Experimental lattice parameters are reproduced with an error margin of 0.5%-4.3%. Cooperative Jahn-Teller distortions are reproduced for MnF3 , but also found in TiF3 and CoF3 at smaller levels compared to MnF3 . Trends in electronic structure with respect to positions of the d bands are linked to the magnetic properties where M = Ti-Cr are weak magnetic Mott-Hubbard insulators, M = Fe-Ni are strong magnetic charge-transfer insulators and MnF3 falls in between. Our work contributes to the characterization of the relatively unknown NiF3 , since FeF3 and CoF3 have similar electronic and magnetic properties. However, NiF3 does not show a Jahn-Teller distortion as present in CoF3 . © 2019 Wiley Periodicals, Inc.
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Affiliation(s)
- Stefan Mattsson
- Institute of Chemistry and Biochemistry, Physical and Theoretical Chemistry, Freie Universität Berlin, Takustr. 3, 14195, Berlin, Germany
| | - Beate Paulus
- Institute of Chemistry and Biochemistry, Physical and Theoretical Chemistry, Freie Universität Berlin, Takustr. 3, 14195, Berlin, Germany
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6
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Liu J, Hejazi K, Balents L. Floquet Engineering of Multiorbital Mott Insulators: Applications to Orthorhombic Titanates. PHYSICAL REVIEW LETTERS 2018; 121:107201. [PMID: 30240238 DOI: 10.1103/physrevlett.121.107201] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Indexed: 06/08/2023]
Abstract
We consider driving multiorbital Mott insulators using laser radiation. We derive general expressions for periodically driven spin-orbital models using time-dependent perturbation theory in the strong interaction limit. We show that the effective exchange interactions of the Floquet spin-orbital Hamiltonian are highly tunable via variations of the frequency, amplitude, and polarization of the laser. We also take the effect of a finite bandwidth of excitations into account and study possible heating effects. We further apply our formalism to orthorhombic titanates YTiO_{3} and LaTiO_{3} based on first-principles calculations, and we find that the spin exchange interactions in these compounds can be engineered to a large extent by tuning the frequency and electric-field amplitude of the laser.
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Affiliation(s)
- Jianpeng Liu
- Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA
| | - Kasra Hejazi
- Department of Physics, University of California, Santa Barbara, California 93106, USA
| | - Leon Balents
- Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA
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7
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Lee K, Youn Y, Han S. Identification of ground-state spin ordering in antiferromagnetic transition metal oxides using the Ising model and a genetic algorithm. SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 2017; 18:246-252. [PMID: 28458746 PMCID: PMC5402741 DOI: 10.1080/14686996.2017.1300046] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/15/2016] [Revised: 12/21/2016] [Accepted: 02/23/2017] [Indexed: 06/07/2023]
Abstract
We identify ground-state collinear spin ordering in various antiferromagnetic transition metal oxides by constructing the Ising model from first-principles results and applying a genetic algorithm to find its minimum energy state. The present method can correctly reproduce the ground state of well-known antiferromagnetic oxides such as NiO, Fe2O3, Cr2O3 and MnO2. Furthermore, we identify the ground-state spin ordering in more complicated materials such as Mn3O4 and CoCr2O4.
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Affiliation(s)
- Kyuhyun Lee
- Department of Materials Science and Engineering and Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
| | - Yong Youn
- Department of Materials Science and Engineering and Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
| | - Seungwu Han
- Department of Materials Science and Engineering and Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
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8
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Wu M, Zheng JC, Wang HQ. Investigation of the multiplet structures and crystal field effects of a TiO6 3d
1 cluster based on configuration interaction calculations. J Appl Crystallogr 2017. [DOI: 10.1107/s160057671700334x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Configuration interaction cluster calculation can effectively reproduce the experimentally measured Ti L
23-edge absorption spectrum for the TiO6 cluster LaTiO3. A further investigation of the hybridization strength and charge-transfer energy effects on the multiplet structures suggests that LaTiO3 should be classified as an intermediate state between the charge-transfer and Mott–Hubbard regimes. Detailed temperature-dependent simulations of absorption spectra support the lifting of Ti t
2g
orbital degeneracy and crystal field splitting. The spin–orbit coupling scenario is ruled out, even though 3d spin–orbit coupling can reproduce the experimental spectrum without including temperature. A combined polarization- and crystal-field-splitting-dependent analysis indicates asymmetric ΔCF–orbital interactions for the TiO6 cluster [Ti3+:3d
1(t
2g
1)], different from the orbital–lattice interactions reported for the NiO6 cluster [Ni3+:3d
7(t
2g
6
eg
1)]. The orbital polarization is defined in terms of the normalized electron occupancies in orbitals with xy and xz(yz) symmetries, and nearly complete orbital polarization (more than 75%) is observed, indicating strongly reduced orbital fluctuations due to the correlation effects. This is consistent with the density of states for titanates based on local density approximation plus dynamical mean-field theory calculations.
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9
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Chen Y, Cui Y, Yao JE. Dielectric characteristics of Fe-doped LaTiO 3+δ and visible light modulation. RSC Adv 2016. [DOI: 10.1039/c6ra22168h] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Fe-doped La1−xFexTiO3+δ (x = 0.05, 0.1, and 0.3, 0.4) ceramic samples were prepared via traditional solid-state reaction route, in which the dielectric properties of visible light modulation were found at room temperature in the measured frequency range.
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Affiliation(s)
- Yan Chen
- Key Laboratory of Micro-Nano Measurement-Manipulation and Physics
- Ministry of Education
- Beihang University
- Beijing 100191
- China
| | - Yimin Cui
- Key Laboratory of Micro-Nano Measurement-Manipulation and Physics
- Ministry of Education
- Beihang University
- Beijing 100191
- China
| | - Jun-en Yao
- Key Laboratory of Micro-Nano Measurement-Manipulation and Physics
- Ministry of Education
- Beihang University
- Beijing 100191
- China
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10
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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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11
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Phototunable magnetism in copper octacyanomolybdate. ScientificWorldJournal 2014; 2014:762765. [PMID: 24895661 PMCID: PMC4034506 DOI: 10.1155/2014/762765] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2014] [Accepted: 03/10/2014] [Indexed: 11/18/2022] Open
Abstract
We introduce copper molybdenum cyanides of general formula Cu2[Mo(CN)8]·nH2O, which can serve as optofunctional magnetic devices. Their ground states generally stay paramagnetic down to temperatures of the K order but exhibit a spontaneous magnetization upon photoirradiation usually below a few tens of K. To interest us still further, such a ferromagnetic stateinduced by blue-laser irradiation is demagnetized step by step through further application of red or near-infrared laser pulses. We solve this intriguing photomagnetism. The ground-state properties are fully revealed by means of a group-theoretical technique. Taking account of experimental observations, we simulate applying pump laser pulses to a likely ground state and successfully reproduce both the magnetization and demagnetization dynamics. We monitor the photorelaxation process through angle-resolved photoemission spectroscopy. Electrons are fully itinerant in any of the photoinduced steady states, forming a striking contrast to the initial equilibrium state of atomic aspect. The fully demagnetized final steady state looks completely different from the initial paramagnetism but bears good analogy to one of the possible ground states available with the Coulomb repulsion on Cu sites suppressed.
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12
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Ishiguro Y, Kimura K, Nakatsuji S, Tsutsui S, Baron AQR, Kimura T, Wakabayashi Y. Dynamical spin–orbital correlation in the frustrated magnet Ba3CuSb2O9. Nat Commun 2013; 4:2022. [PMID: 23771213 DOI: 10.1038/ncomms3022] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2013] [Accepted: 05/17/2013] [Indexed: 11/09/2022] Open
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13
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Garcia-Barriocanal J, Cezar J, Bruno F, Thakur P, Brookes N, Utfeld C, Rivera-Calzada A, Giblin S, Taylor J, Duffy J, Dugdale S, Nakamura T, Kodama K, Leon C, Okamoto S, Santamaria J. Spin and orbital Ti magnetism at LaMnO3/SrTiO3 interfaces. Nat Commun 2010; 1:82. [DOI: 10.1038/ncomms1080] [Citation(s) in RCA: 148] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2010] [Accepted: 08/24/2010] [Indexed: 11/09/2022] Open
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14
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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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15
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Ulrich C, Ament LJP, Ghiringhelli G, Braicovich L, Moretti Sala M, Pezzotta N, Schmitt T, Khaliullin G, van den Brink J, Roth H, Lorenz T, Keimer B. Momentum dependence of orbital excitations in Mott-insulating titanates. PHYSICAL REVIEW LETTERS 2009; 103:107205. [PMID: 19792341 DOI: 10.1103/physrevlett.103.107205] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2009] [Indexed: 05/28/2023]
Abstract
High-resolution resonant inelastic x-ray scattering has been used to determine the momentum dependence of orbital excitations in Mott-insulating LaTiO(3) and YTiO(3) over a wide range of the Brillouin zone. The data are compared to calculations in the framework of lattice-driven and superexchange-driven orbital ordering models. A superexchange model in which the experimentally observed modes are attributed to two-orbiton excitations yields the best description of the data.
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Affiliation(s)
- C Ulrich
- Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany
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16
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Jackeli G, Khaliullin G. Mott insulators in the strong spin-orbit coupling limit: from Heisenberg to a quantum compass and Kitaev models. PHYSICAL REVIEW LETTERS 2009; 102:017205. [PMID: 19257237 DOI: 10.1103/physrevlett.102.017205] [Citation(s) in RCA: 387] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2008] [Indexed: 05/13/2023]
Abstract
We study the magnetic interactions in Mott-Hubbard systems with partially filled t_{2g} levels and with strong spin-orbit coupling. The latter entangles the spin and orbital spaces, and leads to a rich variety of the low energy Hamiltonians that extrapolate from the Heisenberg to a quantum compass model depending on the lattice geometry. This gives way to "engineer" in such Mott insulators an exactly solvable spin model by Kitaev relevant for quantum computation. We, finally, explain "weak" ferromagnetism, with an anomalously large ferromagnetic moment, in Sr2IrO4.
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Affiliation(s)
- G Jackeli
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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17
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Romano A, Noce C, Amendola ME. High-spin magnetic states in the two-orbital Hubbard model on a tetrahedron. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2008; 20:465216. [PMID: 21693855 DOI: 10.1088/0953-8984/20/46/465216] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We present a study of the two-orbital degenerate Hubbard model in which the exact numerical solution on a regular tetrahedron is obtained via suitable implementation of the symmetries generated by the spin, the pairing and the orbital pseudospin operators. In particular, we show that a large variety of high-spin magnetic ground states can develop away from half filling, depending on the values of the electron density and the parameters of the model. As the tetrahedron is the simplest finite-size cluster where hopping processes connect all pairs of sites with constant probability, the study is extended by providing the exact analytical solution of the model on an infinite lattice in the unconstrained hopping limit.
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Affiliation(s)
- Alfonso Romano
- Laboratorio Regionale SuperMat, INFM-CNR, Salerno, Italy. Dipartimento di Fisica 'E. R. Caianiello', Università di Salerno, I-84081 Baronissi (Salerno), Italy
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18
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Baker PJ, Lancaster T, Blundell SJ, Hayes W, Pratt FL, Itoh M, Kuroiwa S, Akimitsu J. Muon spin relaxation study of LaTiO(3) and YTiO(3). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2008; 20:465203. [PMID: 21693843 DOI: 10.1088/0953-8984/20/46/465203] [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 report muon spin relaxation (μSR) measurements on two Ti(3+) containing perovskites, LaTiO(3) and YTiO(3), which display long-range magnetic order at low temperature. For both materials, oscillations in the time dependence of the muon polarization are observed which are consistent with three-dimensional magnetic order. From our data we identify two magnetically inequivalent muon stopping sites. The μSR results are compared with the magnetic structures of these compounds previously derived from neutron diffraction and μSR studies on structurally similar compounds.
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Affiliation(s)
- P J Baker
- Department of Physics, Oxford University, Parks Road, Oxford OX1 3PU, UK
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19
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Cheng JG, Sui Y, Zhou JS, Goodenough JB, Su WH. Transition from orbital liquid to Jahn-Teller insulator in orthorhombic perovskites RTiO3. PHYSICAL REVIEW LETTERS 2008; 101:087205. [PMID: 18764657 DOI: 10.1103/physrevlett.101.087205] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Indexed: 05/21/2023]
Abstract
Following the same strategy used for RVO3, thermal conductivity measurements have been made on a series of single-crystal perovskites RTiO3 (R=La,Nd,...,Yb). Results reveal explicitly a transition from an orbital liquid to an orbitally ordered phase at a magnetic transition temperature, which is common for both the antiferromagnetic and ferromagnetic phases in the phase diagram of RTiO3. This spin/orbital transition is consistent with the mode softening at T_{N} in antiferromagnetic LaTiO3 and is supported by an anomalous critical behavior at T_{c} in ferromagnetic YTiO3.
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Affiliation(s)
- J-G Cheng
- Center for Condensed Matter Science and Technology, Department of Physics, Harbin Institute of Technology, Harbin, 150001, China
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20
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Daghofer M, Wohlfeld K, Oleś AM, Arrigoni E, Horsch P. Absence of hole confinement in transition-metal oxides with orbital degeneracy. PHYSICAL REVIEW LETTERS 2008; 100:066403. [PMID: 18352494 DOI: 10.1103/physrevlett.100.066403] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2007] [Indexed: 05/26/2023]
Abstract
We investigate the spectral properties of a hole moving in a two-dimensional Hubbard model for strongly correlated t(2g) electrons. Although superexchange interactions are Ising-like, a quasi-one-dimensional coherent hole motion arises due to effective three-site terms. This mechanism is fundamentally different from the hole motion via quantum fluctuations in the conventional spin model with SU(2) symmetry. The orbital model describes also propagation of a hole in some e(g) compounds, and we argue that orbital degeneracy alone does not lead to hole self-localization.
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Affiliation(s)
- Maria Daghofer
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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21
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Fujioka J, Miyasaka S, Tokura Y. Doping variation of orbitally induced anisotropy in the electronic structure of La1-xSrxVO3. PHYSICAL REVIEW LETTERS 2006; 97:196401. [PMID: 17155646 DOI: 10.1103/physrevlett.97.196401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2006] [Indexed: 05/12/2023]
Abstract
The variation of anisotropic charge dynamics in the course of a filling-control insulator-metal transition (IMT) in La(1-x)Sr(x)VO3 has been investigated by measurements of optical conductivity spectra with the focus on the role of the t(2g)-orbital degree of freedom. The orbitally induced anisotropic feature of the Mott-gap excitation as well as of the doping-induced midinfrared excitation is suppressed with increasing x, and instead the isotropic and incoherent dynamics of the doped hole dominates over the low-energy excitation near and above the IMT point.
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Affiliation(s)
- J Fujioka
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
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22
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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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23
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Oleś AM, Horsch P, Feiner LF, Khaliullin G. Spin-orbital entanglement and violation of the Goodenough-Kanamori rules. PHYSICAL REVIEW LETTERS 2006; 96:147205. [PMID: 16712118 DOI: 10.1103/physrevlett.96.147205] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2005] [Indexed: 05/09/2023]
Abstract
We point out that large composite spin-orbital fluctuations in Mott insulators with t(2g) orbital degeneracy are a manifestation of quantum entanglement of spin and orbital variables. This results in a dynamical nature of the spin superexchange interactions, which fluctuate over positive and negative values, and leads to an apparent violation of the Goodenough-Kanamori rules.
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Affiliation(s)
- Andrzej M Oleś
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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24
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Miyasaka S, Onoda S, Okimoto Y, Fujioka J, Iwama M, Nagaosa N, Tokura Y. One-dimensional orbital excitations in vanadium oxides. PHYSICAL REVIEW LETTERS 2005; 94:076405. [PMID: 15783836 DOI: 10.1103/physrevlett.94.076405] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2004] [Revised: 10/20/2004] [Indexed: 05/24/2023]
Abstract
The d electron orbital is a hidden but important degree of freedom controlling novel properties of transition-metal oxides. A one-dimensional orbital system is especially intriguing due to its enhanced quantum fluctuation. We present a combined experimental and theoretical study on the Raman scattering spectra in perovskite oxides NdVO(3) and LaVO(3) to prove that the quasi-one-dimensional orbital chain described by fermionic pseudospinons bears orbital excitations exchanging occupied orbital states on the neighboring sites, termed a two-orbiton in analogy with two-magnon.
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Affiliation(s)
- S Miyasaka
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
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25
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Haverkort MW, Hu Z, Tanaka A, Ghiringhelli G, Roth H, Cwik M, Lorenz T, Schüssler-Langeheine C, Streltsov SV, Mylnikova AS, Anisimov VI, de Nadai C, Brookes NB, Hsieh HH, Lin HJ, Chen CT, Mizokawa T, Taguchi Y, Tokura Y, Khomskii DI, Tjeng LH. Determination of the orbital moment and crystal-field splitting in LaTiO3. PHYSICAL REVIEW LETTERS 2005; 94:056401. [PMID: 15783666 DOI: 10.1103/physrevlett.94.056401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2004] [Indexed: 05/24/2023]
Abstract
Utilizing a sum rule in a spin-resolved photoelectron spectroscopic experiment with circularly polarized light, we show that the orbital moment in LaTiO3 is strongly reduced from its ionic value, both below and above the Ne el temperature. Using Ti L2,3 x-ray absorption spectroscopy as a local probe, we found that the crystal-field splitting in the t2g subshell is about 0.12-0.30 eV. This large splitting does not facilitate the formation of an orbital liquid.
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Affiliation(s)
- M W Haverkort
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
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26
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Mishra A, Ma M, Zhang FC, Guertler S, Tang LH, Wan S. Directional ordering of fluctuations in a two-dimensional compass model. PHYSICAL REVIEW LETTERS 2004; 93:207201. [PMID: 15600961 DOI: 10.1103/physrevlett.93.207201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2004] [Indexed: 05/24/2023]
Abstract
In the Mott insulating phase of the transition metal oxides, the effective orbital-orbital interaction is directional both in orbital space and in real space. We discuss a classical realization of directional coupling in two dimensions. Despite extensive degeneracy of the ground state, the model exhibits partial orbital ordering in the form of directional ordering of fluctuations at low temperatures stabilized by an entropy gap. Transition to the disordered phase is shown to be in the Ising universality class through exact mapping and multicanonical Monte Carlo simulations.
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Affiliation(s)
- Anup Mishra
- Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221-0011, USA
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27
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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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28
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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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29
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Fritsch V, Hemberger J, Büttgen N, Scheidt EW, Krug von Nidda HA, Loidl A, Tsurkan V. Spin and orbital frustration in MnSc2S4 and FeSc2S4. PHYSICAL REVIEW LETTERS 2004; 92:116401. [PMID: 15089155 DOI: 10.1103/physrevlett.92.116401] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2003] [Indexed: 05/24/2023]
Abstract
Crystal structure, magnetic susceptibility, and specific heat were measured in the normal cubic spinel compounds MnSc2S4 and FeSc2S4. Down to the lowest temperatures, both compounds remain cubic and reveal strong magnetic frustration. Specifically the Fe compound is characterized by a Curie-Weiss (CW) temperature ThetaCW = -45 K and does not show any indications of order down to 50 mK. In addition, the Jahn-Teller ion Fe2+ is orbitally frustrated. Hence, FeSc2S4 belongs to the rare class of spin-orbital liquids. MnSc2S4 is a spin liquid for temperatures T>TN approximately 2 K.
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Affiliation(s)
- V Fritsch
- Experimentalphysik V, Center for Electronic Correlations and Magnetism, Institut für Physik, Universität Augsburg, D-86159 Augsburg, Germany
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30
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Kim MW, Lee YS, Noh TW, Yu J, Moritomo Y. Optical-spectroscopic detection of spin-exchange interaction pyrochlore molybdates. PHYSICAL REVIEW LETTERS 2004; 92:027202. [PMID: 14753965 DOI: 10.1103/physrevlett.92.027202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2003] [Indexed: 05/24/2023]
Abstract
Optical spectroscopy was used to determine nearest-neighbor spin correlations in pyrochlore molybdates R2Mo2O7 (R=Y, Sm, and Nd), which exhibit ferromagnetic metal to spin-glass insulator transition as the R ion size decreases. Using an analysis based on the orbitally degenerate Hubbard model, we could estimate important physical parameters, such as the effective on-site Coulomb energy U(eff) and the Hund rule exchange coupling J(H). We demonstrated experimentally and theoretically that the effective superexchange interaction between the Mo ions depends on J(H)/U(eff), which determines the phase boundary of the magnetic ground states.
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Affiliation(s)
- M W Kim
- ReCOE & School of Physics, Seoul National University, Seoul 151-747, Korea
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31
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32
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Horsch P, Khaliullin G, Oleś AM. Dimerization versus orbital-moment ordering in a Mott insulator YVO3. PHYSICAL REVIEW LETTERS 2003; 91:257203. [PMID: 14754147 DOI: 10.1103/physrevlett.91.257203] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2002] [Indexed: 05/24/2023]
Abstract
We use exact diagonalization combined with mean-field theory to investigate the phase diagram of the spin-orbital model for cubic vanadates. The spin-orbit coupling competes with Hund's exchange and triggers a novel phase, with the ordering of t(2g) orbital magnetic moments stabilized by the tilting of VO6 octahedra. It explains qualitatively spin canting and reduction of magnetization observed in YVO3. At finite temperature, an orbital instability in the C-type antiferromagnetic phase induces modulation of magnetic exchange constants even in the absence of lattice distortions. The calculated spin structure factor shows a magnon splitting at q-->=(0,0,pi / 2) due to the orbital dimerization.
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Affiliation(s)
- Peter Horsch
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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33
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Mochizuki M, Imada M. Orbital-spin structure and lattice coupling in RTiO3 where R=La, Pr, Nd, and Sm. PHYSICAL REVIEW LETTERS 2003; 91:167203. [PMID: 14611435 DOI: 10.1103/physrevlett.91.167203] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2002] [Indexed: 05/24/2023]
Abstract
The origin of the G-type antiferromagnetism [AFM(G)] and puzzling properties of RTiO3 with R=La are studied. We clarify that the crystal field from La caused by the GdFeO3-type distortion lifts the t(2g) degeneracy at Ti 3d orbitals. The lift stabilizes the AFM(G) with spin-exchange constant in agreement with neutron-scattering results. The orbital-spin structures for R=Pr, Nd, and Sm are also consistent with experiments. We propose that the GdFeO3-type distortion has a universal mechanism of controlling orbital-spin structure competing with the Jahn-Teller (JT) mechanism.
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Affiliation(s)
- Masahito Mochizuki
- Institute for Solid State Physics, University of Tokyo, Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
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34
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Kiyama T, Itoh M. Presence of 3d quadrupole moment in LaTiO3 studied by 47,49Ti NMR. PHYSICAL REVIEW LETTERS 2003; 91:167202. [PMID: 14611434 DOI: 10.1103/physrevlett.91.167202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2003] [Indexed: 05/24/2023]
Abstract
47,49Ti NMR spectra of LaTiO3 are reexamined and the orbital state of this compound is discussed. The NMR spectra of LaTiO3 taken at 1.5 K under zero external field indicate a large nuclear quadrupole splitting. This splitting is ascribed to the presence of the rather large quadrupole moment of 3d electrons at Ti sites, suggesting that the orbital liquid model proposed for LaTiO3 is inappropriate. The NMR spectra are well explained by the orbital ordering model expressed approximately as 1/square root of 3(d(xy)+d(yz)+d(zx)) originating from a crystal field effect. It is also shown that most of the orbital moment is quenched.
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Affiliation(s)
- Takashi Kiyama
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
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35
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Harris AB, Yildirim T, Aharony A, Entin-Wohlman O, Korenblit IY. Unusual symmetries in the Kugel-Khomskii Hamiltonian. PHYSICAL REVIEW LETTERS 2003; 91:087206. [PMID: 14525275 DOI: 10.1103/physrevlett.91.087206] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2002] [Indexed: 05/24/2023]
Abstract
The Kugel-Khomskii Hamiltonian for cubic titanates describes spin and orbital superexchange interactions between d(1) ions having threefold degenerate t(2g) orbitals. Since orbitals do not couple along "inactive" axes, perpendicular to the orbital planes, the total number of electrons in |alpha> orbitals in any such plane and the corresponding total spin are both conserved. A Mermin-Wagner construction shows that there is no long-range spin ordering at nonzero temperatures. Inclusion of spin-orbit coupling allows such ordering, but even then the excitation spectrum is gapless due to a continuous symmetry. Thus, the observed order and gap require more symmetry breaking terms.
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Affiliation(s)
- A B Harris
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
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36
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37
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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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38
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Khaliullin G, Okamoto S. Quantum behavior of orbitals in ferromagnetic titanates: novel orderings and excitations. PHYSICAL REVIEW LETTERS 2002; 89:167201. [PMID: 12398749 DOI: 10.1103/physrevlett.89.167201] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2002] [Indexed: 05/24/2023]
Abstract
We investigate the collective behavior of orbital angular momentum in the spin ferromagnetic state of a Mott insulator with t(2g) orbital degeneracy. The frustrated nature of the interactions leads to an infinite degeneracy of classical states. Quantum effects select four distinct orbital orderings. Two of them have a quadrupolar order, while the other states show in addition weak orbital magnetism. Specific predictions are made for neutron scattering experiments which might help to identify the orbital order in YTiO3 and to detect the elementary orbital excitations.
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Affiliation(s)
- Giniyat Khaliullin
- Max-Planck-Institut für Festkorperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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39
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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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40
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Loa I, Adler P, Grzechnik A, Syassen K, Schwarz U, Hanfland M, Rozenberg GK, Gorodetsky P, Pasternak MP. Pressure-induced quenching of the Jahn-Teller distortion and insulator-to-metal transition in LaMnO(3). PHYSICAL REVIEW LETTERS 2001; 87:125501. [PMID: 11580518 DOI: 10.1103/physrevlett.87.125501] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2001] [Indexed: 05/23/2023]
Abstract
LaMnO(3) was studied by synchrotron x-ray diffraction, optical spectroscopies, and transport measurements under pressures up to 40 GPa. The cooperative Jahn-Teller (JT) distortion is continuously reduced with increasing pressure. There is strong indication that the JT effect and the concomitant orbital order are completely suppressed above 18 GPa. The system, however, retains its insulating state to approximately 32 GPa, where it undergoes a bandwidth-driven insulator-metal transition. Delocalization of electron states, which suppresses the JT effect but is insufficient to make the system metallic, appears to be a key feature of LaMnO(3) at 20-30 GPa.
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Affiliation(s)
- I Loa
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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Khaliullin G, Horsch P, Oleś AM. Spin order due to orbital fluctuations: cubic vanadates. PHYSICAL REVIEW LETTERS 2001; 86:3879-3882. [PMID: 11329347 DOI: 10.1103/physrevlett.86.3879] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2000] [Indexed: 05/23/2023]
Abstract
We investigate the highly frustrated spin and orbital superexchange interactions in cubic vanadates. The fluctuations of t(2g) orbitals trigger a novel mechanism of ferromagnetic interactions between spins S = 1 of V3+ ions along one of the cubic directions which operates already in the absence of Hund's rule exchange J(H), and leads to the C-type antiferromagnetic phase in LaVO3. The Jahn-Teller effect can stabilize the orbital ordering and the G-type antiferromagnetic phase at low temperatures, but large entropy due to orbital fluctuations favors again the C phase at higher temperatures, as observed in YVO (3).
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Affiliation(s)
- G Khaliullin
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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Khaliullin G, Maekawa S. Orbital liquid in three-dimensional mott insulator: LaTiO3. PHYSICAL REVIEW LETTERS 2000; 85:3950-3953. [PMID: 11041968 DOI: 10.1103/physrevlett.85.3950] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2000] [Indexed: 05/23/2023]
Abstract
We present a theory of spin and orbital states in Mott insulator LaTiO3. The spin-orbital superexchange interaction between d(1)(t(2g)) ions in cubic crystal suffers from a pathological degeneracy of orbital states at the classical level. Quantum effects remove this degeneracy and result in the formation of the coherent ground state, in which the orbital moment of t(2g) level is fully quenched. We find a finite gap for orbital excitations. Such a disordered state of local degrees of freedom on unfrustrated, simple cubic lattice is highly unusual. Orbital liquid state naturally explains observed anomalies of LaTiO3.
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Affiliation(s)
- G Khaliullin
- Max-Planck-Institut fur Festkorperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany and Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
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