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BiS 2 compounds: Properties, effective low-energy models and RPA results

BiS 2 compounds: Properties, effective low-energy models and RPA results . George Martins (Oakland University) Adriana Moreo (Oak Ridge and Univ. Tennessee) Elbio Dagotto (Oak Ridge and Univ. Tennessee ). Martins , Moreo , and Dagotto PRB 8 7 , 081102 1(R ) ( 201 3 ).

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BiS 2 compounds: Properties, effective low-energy models and RPA results

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  1. BiS2 compounds: Properties, effective low-energy models and RPA results George Martins (Oakland University) Adriana Moreo (Oak Ridge and Univ. Tennessee) Elbio Dagotto (Oak Ridge and Univ. Tennessee) Martins, Moreo, and Dagotto PRB 87, 0811021(R) (2013) Supported by DOE through Oak Ridge Nat. Lab. International Workshop on Recent Developments in Fe-based HTcSuperconductors Long Island 6th September 2013

  2. BiS2 –based family of superconductors • Basic properties • Experimental results (brief summary) • Band structure (2-band effective model) • Phonons or unconventional? • RPA results • Fermi surface nesting: • Peculiar pairing properties: A1g and B2g are degenerate. • Much more research is needed.

  3. First observations in Bi4O4S3 Tc = 8.6K

  4. Crystal structure for Bi4O4S3 Tetragonal layered structure Charge reservoir

  5. Physical properties V.P.S. Awana, JACS (2012) Metallic But non-Fermi liquid Shielding fraction ~ 95% Polycrystalline samples…

  6. Electron doping: LaO(F)BiS2 Electron doping V.P.S. Awana et al. Sol. St. Comm. 157 (2013) 21

  7. Superconducting dome K. Deguchi et al., EPL 101, 17004 (2013)

  8. Electron doping: La1-xMxOBiS2 Electron doping M. B. Maple et al., PRB 87, 174512 (2013)

  9. Hydrostatic pressure M. B. Maple et al., arXiv:1308.1072

  10. Phonons?

  11. Unconventional? arXiv:1207.4955 Transport and magnetization measurements

  12. Downfolding procedure 6 Bi 6p, 12 S 3p, 6 O 2p Full DFT calculation for LaOBiS2 2 Bi 6p 2 S 3p 1 layer 2 Bi 6p 2 S 3p 2 layers H. Usui, K. Suzuki, and K. Kuroki PRB 86, 220501(R) (2012)

  13. Band structure Semiconductor to metal transition with electron doping holepockets

  14. 2d view of the bands

  15. Fermi surface nesting

  16. RPA calculation for multi-band model Bi 6p orbital Lindhardfunction (irreduciblesusceptibility) NJP 11 (2009) 025016 and references [36] and [37].

  17. Spin/charge susceptibility

  18. Introducing interactions Hund’s coupling Coulomb inter-orbital Coulomb intra-orbital pair hopping inter-orbital 4x4 matrix involving all many-body terms. Dyson-type equations: charge (orbital) spin

  19. RPA spin susceptibility

  20. RPA spin susceptibility

  21. Obtaining the RPA pairing functions eigenvalue problem, with matrix indexes k and k’ gap function gα associated to largest eigenvalue will have the highest Tc projected pairing interaction singlet pairing interaction charge spin very pronounced peak at incommensurate k vector

  22. Pairing functions

  23. Competition between A1g and B2g

  24. Intra-band scattering

  25. Nesting and pairing

  26. Conclusions • Properties of new BiS2-based SC family was presented: • Layered material • Semiconducting /metallic • 2 6p bands minimum model • Phonons or unconventional? • RPA results show: • Magnetic fluctuations dominate • Pairing is highly dependent on nesting • A1g (no nodes) and B2g (nodal) are degenearte

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