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Title: Electron-phonon superconductivity in LaO{sub 0.5}F{sub 0.5}BiSe{sub 2}

Abstract

We report density functional calculations of the electronic structure, Fermi surface, phonon spectrum and electron–phonon coupling for the newly discovered superconductor LaO{sub 0.5}F{sub 0.5}BiSe{sub 2}. It is confirmed that there is a strong Fermi surface nesting at (π,π,0), which results in unstable phonon branches. Combining the frozen phonon total energy calculations and an anharmonic oscillator model, we find that the quantum fluctuation prevents the appearance of static long–range order. The calculation shows that LaO{sub 0.5}F{sub 0.5}BiSe{sub 2} is highly anisotropic, and same as its cousin LaO{sub 0.5}F{sub 0.5}BiS{sub 2}, this compound is also a conventional electron-phonon coupling induced superconductor.

Authors:
; ; ;  [1];  [2];  [3];  [2];  [4]
  1. Department of Physics and National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China)
  2. Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200062 (China)
  3. Department of Physics, University of California, Davis, One Shields Avenue, Davis, California 95616 (United States)
  4. (China)
Publication Date:
OSTI Identifier:
22304010
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 23; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANHARMONIC OSCILLATORS; ANISOTROPY; BISMUTH COMPOUNDS; DENSITY FUNCTIONAL METHOD; ELECTRONIC STRUCTURE; ELECTRON-PHONON COUPLING; FERMI LEVEL; FLUCTUATIONS; FLUORINE COMPOUNDS; LANTHANUM COMPOUNDS; OXYGEN COMPOUNDS; SELENIUM COMPOUNDS; SPECTRA; SUPERCONDUCTIVITY; SUPERCONDUCTORS

Citation Formats

Feng, Yanqing, Du, Yongping, Wan, Xiangang, E-mail: xgwan@nju.edu.cn, Wang, Bogen, Ding, Hang-Chen, Savrasov, Sergey Y., Duan, Chun-Gang, and National Laboratory for Infrared Physics, Chinese Academy of Sciences, Shanghai 200083. Electron-phonon superconductivity in LaO{sub 0.5}F{sub 0.5}BiSe{sub 2}. United States: N. p., 2014. Web. doi:10.1063/1.4883755.
Feng, Yanqing, Du, Yongping, Wan, Xiangang, E-mail: xgwan@nju.edu.cn, Wang, Bogen, Ding, Hang-Chen, Savrasov, Sergey Y., Duan, Chun-Gang, & National Laboratory for Infrared Physics, Chinese Academy of Sciences, Shanghai 200083. Electron-phonon superconductivity in LaO{sub 0.5}F{sub 0.5}BiSe{sub 2}. United States. doi:10.1063/1.4883755.
Feng, Yanqing, Du, Yongping, Wan, Xiangang, E-mail: xgwan@nju.edu.cn, Wang, Bogen, Ding, Hang-Chen, Savrasov, Sergey Y., Duan, Chun-Gang, and National Laboratory for Infrared Physics, Chinese Academy of Sciences, Shanghai 200083. 2014. "Electron-phonon superconductivity in LaO{sub 0.5}F{sub 0.5}BiSe{sub 2}". United States. doi:10.1063/1.4883755.
@article{osti_22304010,
title = {Electron-phonon superconductivity in LaO{sub 0.5}F{sub 0.5}BiSe{sub 2}},
author = {Feng, Yanqing and Du, Yongping and Wan, Xiangang, E-mail: xgwan@nju.edu.cn and Wang, Bogen and Ding, Hang-Chen and Savrasov, Sergey Y. and Duan, Chun-Gang and National Laboratory for Infrared Physics, Chinese Academy of Sciences, Shanghai 200083},
abstractNote = {We report density functional calculations of the electronic structure, Fermi surface, phonon spectrum and electron–phonon coupling for the newly discovered superconductor LaO{sub 0.5}F{sub 0.5}BiSe{sub 2}. It is confirmed that there is a strong Fermi surface nesting at (π,π,0), which results in unstable phonon branches. Combining the frozen phonon total energy calculations and an anharmonic oscillator model, we find that the quantum fluctuation prevents the appearance of static long–range order. The calculation shows that LaO{sub 0.5}F{sub 0.5}BiSe{sub 2} is highly anisotropic, and same as its cousin LaO{sub 0.5}F{sub 0.5}BiS{sub 2}, this compound is also a conventional electron-phonon coupling induced superconductor.},
doi = {10.1063/1.4883755},
journal = {Journal of Applied Physics},
number = 23,
volume = 115,
place = {United States},
year = 2014,
month = 6
}
  • The physical properties of the previously reported superconductor IrGe and the Rh 1-xIr xGe solid solution are investigated. IrGe has an exceptionally high superconducting transition temperature (T c=4.7 K) among the isostructural 1:1 late-metal germanides MGe (M=Rh, Pd, Ir, and Pt). Specific-heat measurements reveal that IrGe has an anomalously low Debye temperature, originating from a low-lying phonon, compared to the other MGe phases. A large jump at T c in the specific-heat data clearly indicates that IrGe is a strong coupling superconductor. In the Rh 1-xIr xGe solid solution, a relationship between an anomalous change in lattice constants and themore » Debye temperature is observed. We conclude that the unusually high T c for IrGe is likely due to strong electron–phonon coupling derived from the presence of a low-lying phonon.« less
  • The new theoretical approach is proposed for studying the coupled states responsible for superconductivity in crystal without using the idea of electron pairing. From the approach it follows that BCS electron-pairing postulates are only approximate. It is shown that superconductivity (SC) coupled states can be created by pairs of electrons with nonzero full momentum and spin (k{sub 1} + k{sub 2} {ne} 0, s + s{prime} {ne} 0). The model numerical calculations have shown that dependence of SC gap (energy of coupled states) on temperature is nonexponential and depends on the momenta of electrons in pair.
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  • The synthesis and physical properties of the new misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2} are reported. Transmission electron microscopy and powder X-ray diffraction show that the structure consists of alternating rock-salt type BiSe layers and hexagonal (TiSe{sub 2}){sub 2} double layers. Resistivity, specific heat, and magnetization measurements show that it has metallic and diamagnetic behaviors. These results are interpreted and discussed in the context of the transition between single-layer (BiSe){sub 1.13}(TiSe{sub 2}), which shows no charge density wave, and infinite-layered (bulk) 1T-TiSe{sub 2}, which undergoes a charge density wave transition at T=202 K. Intercalation with copper, Cu{sub x}(BiSe){sub 1.15}(TiSe{sub 2}){submore » 2}, (0≤x≤0.10) is also reported, but unlike Cu{sub x}TiSe{sub 2}, no superconductivity is observed down to T=0.05 K. Thus, the series Cu{sub x}(BiSe){sub 1+δ}(TiSe{sub 2}){sub n} provides an effective approach to elucidate the impact of dimensionality on charge density wave formation and superconductivity. - Graphical abstract: The newly discovered misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2} shown in the series (BiSe){sub 1+δ}(TiSe{sub 2}){sub n}. Display Omitted - Highlights: • Reports the structure and properties of the new misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2}. • The structure consists of a rock salt type BiSe layer and a double (TiSe{sub 2}){sub 2} layer. • The n=1, 2 misfits (BiSe){sub 1+δ}(TiSe{sub 2}){sub n} are found not to exhibit CDW transitions. • Evidence is presented that there is likely a low-lying CDW excited state. • The series Cu{sub x}(BiSe){sub 1+δ}(TiSe{sub 2}){sub 2} does not superconduct, unlike Cu{sub x}TiSe{sub 2}.« less