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Sarkar S, Raghunathan R, Chowdhury S, Choudhary RJ, Phase DM. The Mystery behind Dynamic Charge Disproportionation in BaBiO 3. NANO LETTERS 2021; 21:8433-8438. [PMID: 34586820 DOI: 10.1021/acs.nanolett.1c03103] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
BaBiO3(BBO) is known to be a valence-skipping perovskite, which avoids the metallic state through charge disproportionation (CD), the mechanism of which is still unresolved. A novel mechanism for CD is presented here in the covalent limit using a molecular orbital (MO) picture under two scenarios: (case i) Bi 6sp-O 2p and (case ii) Bi 6p-O 2p hybridizations that favor 5+ and 3+ states, respectively. The proposed model is further validated by using a combinatorial approach of X-ray spectroscopic experiments and first-principle calculations. The bulk X-ray photoemission spectrum reveals that, at room temperature, the CD is dynamic in nature, whereas, at 200 K, it approaches a quasi-static limit. Under compressive strain, the octahedral breathing mode is damped and drives the system to a quasi-static limit even at room temperature, giving rise to asymmetric CD.
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Affiliation(s)
- Sumit Sarkar
- UGC-DAE Consortium for Scientific Research, Indore 452001, India
| | | | - Sourav Chowdhury
- UGC-DAE Consortium for Scientific Research, Indore 452001, India
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Abstract
A Kene–Mele-type nearest-neighbor tight-binding model on a pyrochlore lattice is known to be a topological insulator in some parameter region. It is an important task to realize a topological insulator in a real compound, especially in an oxide that is stable in air. In this paper we systematically performed band structure calculations for six pyrochlore oxides A2B2O7 (A = Sn, Pb, Tl; B = Nb, Ta), which are properly described by this model, and found that heavily hole-doped Sn2Nb2O7 is a good candidate. Surprisingly, an effective spin–orbit coupling constant λ changes its sign depending on the composition of the material. Furthermore, we calculated the band structure of three virtual pyrochlore oxides, namely In2Nb2O7, In2Ta2O7 and Sn2Zr2O7. We found that Sn2Zr2O7 has a band gap at the k = 0 (Γ) point, similar to Sn2Nb2O7, though the band structure of Sn2Zr2O7 itself differs from the ideal nearest-neighbor tight-binding model. We propose that the co-doped system (In,Sn)2(Nb,Zr)2O7 may become a candidate of the three-dimensional strong topological insulator.
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Wen CHP, Xu HC, Yao Q, Peng R, Niu XH, Chen QY, Liu ZT, Shen DW, Song Q, Lou X, Fang YF, Liu XS, Song YH, Jiao YJ, Duan TF, Wen HH, Dudin P, Kotliar G, Yin ZP, Feng DL. Unveiling the Superconducting Mechanism of Ba_{0.51}K_{0.49}BiO_{3}. PHYSICAL REVIEW LETTERS 2018; 121:117002. [PMID: 30265111 DOI: 10.1103/physrevlett.121.117002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Revised: 07/08/2018] [Indexed: 05/12/2023]
Abstract
The mechanism of high superconducting transition temperatures (T_{c}) in bismuthates remains under debate despite more than 30 years of extensive research. Our angle-resolved photoemission spectroscopy studies on Ba_{0.51}K_{0.49}BiO_{3} reveal an unexpectedly 34% larger bandwidth than in conventional density functional theory calculations. This can be reproduced by calculations that fully account for long-range Coulomb interactions-the first direct demonstration of bandwidth expansion due to the Fock exchange term, a long-accepted and yet uncorroborated fundamental effect in many body physics.Furthermore, we observe an isotropic superconducting gap with 2Δ_{0}/k_{B}T_{c}=3.51±0.05, and strong electron-phonon interactions with a coupling constant λ∼1.3±0.2. These findings solve a long-standing mystery-Ba_{0.51}K_{0.49}BiO_{3} is an extraordinary Bardeen-Cooper-Schrieffer superconductor, where long-range Coulomb interactions expand the bandwidth, enhance electron-phonon coupling, and generate the high T_{c}. Such effects will also be critical for finding new superconductors.
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Affiliation(s)
- C H P Wen
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
| | - H C Xu
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
| | - Q Yao
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
| | - R Peng
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
| | - X H Niu
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
| | - Q Y Chen
- Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang 621908, China
| | - Z T Liu
- CAS Center for Excellence in Superconducting Electronics (CENSE), Shanghai 200050, China
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences, Shanghai 200050, China
| | - D W Shen
- CAS Center for Excellence in Superconducting Electronics (CENSE), Shanghai 200050, China
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences, Shanghai 200050, China
| | - Q Song
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
| | - X Lou
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
| | - Y F Fang
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
| | - X S Liu
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
| | - Y H Song
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
| | - Y J Jiao
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - T F Duan
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - H H Wen
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - P Dudin
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, United Kingdom
| | - G Kotliar
- Department of Physics, Rutgers University, Piscataway, New Jersey 08854, USA
| | - Z P Yin
- Department of Physics and Center for Advanced Quantum Studies, Beijing Normal University, Beijing 100875, China
| | - D L Feng
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200438, People's Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
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Kapcia K, Robaszkiewicz S. The magnetic field induced phase separation in a model of a superconductor with local electron pairing. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:065603. [PMID: 23334285 DOI: 10.1088/0953-8984/25/6/065603] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We have studied the extended Hubbard model with pair hopping in the atomic limit for arbitrary electron density and chemical potential and focus on paramagnetic effects of the external magnetic field. The Hamiltonian considered consists of (i) the effective on-site interaction U and (ii) the intersite charge exchange interactions I, determining the hopping of electron pairs between nearest-neighbour sites. The phase diagrams and thermodynamic properties of this model have been determined within the variational approach (VA), which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. Our investigation of the general case shows that the system can exhibit not only the homogeneous phases-superconducting (SS) and non-ordered (NO)-but also the phase separated states (PS: SS-NO). Depending on the values of interaction parameters, the PS state can occur in higher fields than the SS phase (field induced PS). Some ground state results beyond the VA are also presented.
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Affiliation(s)
- Konrad Kapcia
- Electron States of Solids Division, Faculty of Physics, Adam Mickiewicz University in Poznań, Poznań, Poland.
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Varma CM. Considerations on the mechanisms and transition temperatures of superconductivity induced by electronic fluctuations. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2012; 75:052501. [PMID: 22790584 DOI: 10.1088/0034-4885/75/5/052501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
An overview of the momentum and frequency dependence of effective electron-electron interactions which favor electronic instability to a superconducting state in the angular-momentum channel ℓ and the properties of the interactions which determine the magnitude of the temperature T(c) of the instability is provided. Interactions induced through exchange of electronic fluctuations of spin density, charge density or current density are considered. Special attention is paid to the role of quantum-critical fluctuations (QCFs) including pairing due to their virtual exchange as well as de-pairing due to inelastic scattering. Additional insight is gained by reviewing empirical data and theory specific to superfluidity in liquid He(3), superconductivity in some of the heavy-fermion compounds, in cuprates, in pncitides and the valence skipping compound. The physical basis for the following observation is provided: the ratio of the maximum T(c) to the typical phonon frequency in phonon induced s-wave superconductivity is O(10(-1)); the ratio of p-wave T(c) to the renormalized Fermi energy in liquid He(3), a very strongly correlated Fermi liquid near its melting pressure, is only O(10(-3)); in the cuprates and the heavy fermions where d-wave superconductivity occurs in a region governed by QCFs, this ratio rises to O(10(-2)). These discussions also suggest factors important for obtaining higher T(c). Experiments and theoretical investigations are suggested to clarify the many unresolved issues.
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Affiliation(s)
- C M Varma
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
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Sarker SK, Lair SL. The negative-U Hubbard model with long-range Coulomb interaction: metal-insulator transition far from half-filling. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2005; 17:3885-3894. [PMID: 21690705 DOI: 10.1088/0953-8984/17/25/015] [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
It is shown that a metal-insulator transition can occur far from half-filling in the negative-U Hubbard model in the presence of long-range repulsive interactions. Specifically, we consider the bcc lattice at an electron concentration of 2/3 and show that a CDW insulating state exists which is energetically favoured over the relevant metallic states. The repulsive interaction plays the same role as it does in stabilizing a Wigner crystal. Despite the absence of Fermi surface nesting, the CDW insulator appears at rather small values of the interaction, preceded by a CDW semimetal at even smaller values. This places severe restrictions on the region of the parameter space where superconductivity may exist. We believe that the model will show similar behaviour for other electron densities and other lattices.
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Affiliation(s)
- Sanjoy K Sarker
- Department of Physics, The University of Alabama, Tuscaloosa, AL 35487, USA
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