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Superconductivity in Cu x Bi 2 Se 3

Superconductivity in Cu x Bi 2 Se 3. Wei-Feng Tsai Joint Group Meeting Feb 10, 2010. Ref: (1) Y.S. Hor et al, PRL 104, 057001 (2010) (2) N. Bray-Ali and S. Haas, Physics 3, 11 (2010) (3) L. Wray et al., arXiv:0912.3341. Outline. Motivation Crystal and band structures

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Superconductivity in Cu x Bi 2 Se 3

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  1. Superconductivity in CuxBi2Se3 Wei-Feng Tsai Joint Group Meeting Feb 10, 2010 Ref: (1) Y.S. Hor et al, PRL 104, 057001 (2010) (2) N. Bray-Ali and S. Haas, Physics 3, 11 (2010) (3) L. Wray et al., arXiv:0912.3341

  2. Outline • Motivation • Crystal and band structures • Effect of doping in the normal state • Superconductivity • Discussion on the pairing mechanism

  3. CB SS VB Nutshell of the TRI Topological Insulators • Bulk gap (mainly from SOI, band inversion) • Gapless surface/edge states (topology protected) Physics:Nontrivial GS without spontaneous symmetry breaking Application:Spintronic devices and creating excitations with non-Abelian statistics necessary in making fault-tolerant quantum computers (junction requested!) How to turn a TI into a SC?

  4. Crystal structure of CuxBi2Se3 a=b~4Å c~29Å Compare with Bi2-xCuxSe3: non-superconducting!

  5. ~0.4eV Band structure at T>Tc for Cu0.12Bi2Se3 Massive Dirac-like spectrum for CB; SS are still “well-defined”

  6. Effect of Doping (T>Tc) CuxBi2Se3 (electron doped) • Though c increases, the band gap remains the same • Surface-state dispersion is renormalized (vF is reduced by 30%) • Fermi surface gets anisotropy • Nonlinear doping Bi2-xCuxSe3 (weakly hole doped)→CB is above EF!

  7. Superconductivity (resistivity) CuxBi2Se3 superconducts when 0.1<x<0.15; Bi2-xCuxSe3 doesn’t! X=0.12 ne~2x1020cm-3 Fraction ~ 20% at Tc

  8. Superconductivity (magnetization) • Anisotropic SC: ξab = 140Å, ξc = 52Å as T→0 • GL κ ~ 50: strong type II

  9. STM result (topography) near Tc Intercalated Cu on the surface for 1, subsurface for 2; open question for 3?

  10. Mechanism for Cooper pairing • Electron-phonon? Bend in bulk dispersion near 90meV binding energy • Two possible SC states Parity even (non-Abelian) Parity odd (topological SC) PΔ(k)P = ± Δ(-k) Fu and Berg, arXiv: 0912.3294

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