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The “normal” state of layered dichalcogenides

The “normal” state of layered dichalcogenides. Arghya Taraphder. Department of Physics and Centre for Theoretical Studies. Indian Institute of Technology Kharagpur. Workshop @ Harish Chandra Research Institute, November 12-14, 2010. Salient Features.

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The “normal” state of layered dichalcogenides

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  1. The “normal” state of layered dichalcogenides Arghya Taraphder Department of Physics and Centre for Theoretical Studies Indian Institute of Technology Kharagpur Workshop @ Harish Chandra Research Institute, November 12-14, 2010

  2. Salient Features • Transition metal dichalcogenide – TM atoms separated by two layers of chalcogen atoms TM atoms form 2D triangular lattice • CDW & Superconductivity (likely to be anisotropic) • Partially filled TM d band or chalcogen p band:[]d1/0 • 1T and 2H type lattice structure • Both I and C CDW at moderate temperature • Normal to SC transition with pressure/doping • Normal transport unusual (cf. HTSC)

  3. Dichalcogenides: crystal structure

  4. Glossary

  5. Typical Phase diagram 2H-TaSe2 D.B. Mcwhan, et al. PRL 45,269(1980)(2H-TaSe2) 1T-TiSe2 A. F. Kusmartseva, et al. PRL 103, 236401(2009) (1T-TiSe2) B. Sipos, et al. Nat. mater. 7, 960 (2008) (IT-TaS2) 1T-TaS2

  6. Cava et al. 2H-TaS2

  7. Phase diagram of 1T-TiSe2 : doping and pressure

  8. Quantum critical? Castro-Neto, loc cit Cava, PRL (2008)

  9. DC Resistivities Aebi, loc cit

  10. Resistivity of TMDs: 1T and 2H P. Aebi, et al. Journal of Electron Spectroscopy and Related Phenomena 117–118 (2001) Y. Ueda, et al.Journal of Physical Society of Japan 56 2471-2476, (1987).

  11. 2H-TaSe2 Vescoli et al, PRL 81, 453 (1998)

  12. Optical conductivity (0.04 < E < 5 eV range) R C Dynes, et al., EPJB 33, 15 (2003)

  13. Features of dc transport and Re σ (ω) • “Drude-like” peak at ω=0 for both systems along both ab and • C-directions, narrowing at low T, indicating freezing of • scattering of charge carriers at low energy • Tccdw does not affect transport at all, in fact thermodynamics • is also unaffected • Broad conductivity upto large energies (~0.5 eV)

  14. Dynes loc cit

  15. Spectral weight distribution • Spectral weight is non-zero even upto 5 eV and • beyond – “recovery” of total n uncertain • Shifts progressively towards FIR as T is lowered - • condensation at lower frequency • Nothing abrupt happens as T_CDW is crossed

  16. Transport scattering rate ab-plane

  17. Transport scattering rate c-axis

  18. Scattering rate from transport • Strongly frequency dependent. Rapid suppression • of both Γab and Γc below characteristic freq. ~ 500 /cm • Possible “pseudogap” in 20K curve • High and low T Γab cross each other for TaSe2 • at some frequency • No saturation of Γab upto 0.6 eV • Both Γab and Γc are above Γ= ω line upto 2000 /cm and • nearly linear in ω

  19. “QP” Scattering Rate & SE from ARPES Valla, PRL 85, 4759 (2000)

  20. Fit with momentum-indep. SE Valla, loc. cit..

  21. Electronic structure Aebi, JES 117, 433 (2001)

  22. Self-energy from ARPES • Local - no k-dependence • Re Σ peaks at 65 meV, Im Σ drops there – • characteristic of a photo-hole scattering off a • collective ‘mode’ ~ 65 mev (too large for all phonons • in TaSe2) • Im Σ(0) matches excellently with transport Γ(0) in • its T-dependence

  23. Band structure 2H-TaSe2 H.E. Brauer,et al. J. Phys. Cond. Matter 13, 9879 (2001) Aebi, JES 117, 433 (2001)

  24. Tight Binding Description N V Smith, et al. J. Phys. C:Solid State Phys. 18 (1985) 3175-3189

  25. Tight binding fit near FL for 2H-TaSe2 N V Smith, et al. J. Phys. C: Solid State Phys. 18 (1985) 3175-3189.

  26. Fermi surface map for the TB bands 2H-TaSe2 1T-TaS2

  27. ARPES - 2H-TaSe2 Liu, PRL 80, 5762 (1998)

  28. Liu, PRL 80, 5762 (1998)

  29. Valla et al, PRL 85, 4759 (2000)

  30. CDW Gap ? Castro_Neto, PRL 86, 4382 (2001)

  31. )Pseudogap in 2H-TaSe2, Borisenko et al, PRL 100, 196402 (2008)

  32. Fermi surface and ARPES - 2H type S V Borisenko, et al. Phys. Rev. Lett. 100, 196402 (2008) N V Smith, et al. J. Phys. C: Solid State Phys. 18 (1985) 3175-3189.

  33. Fermi surface and ARPES - 1T type N V Smith, et al. J. Phys. C: Solid State Phys. 18 (1985) 3175-3189. F.Clerc, et al. Physica B 351 245-249, (2004)

  34. Fermi surface of 1T-TiSe2 P. Aebi, et al. Phys.Rev.B 61 16213, (2000)

  35. Superlattice & BZ in the CDW phase of Dichalcogenides 2H-TaSe2 1T-TaS2 N V Smith, et al. J. Phys. C:Solid State Phys. 18 (1985) 3175-3189.

  36. Our Work: LDA - tight binding fit near FL for 2H-TaSe2 N V Smith, et al. J. Phys. C: Solid State Phys. 18 (1985) 3175-3189.

  37. Fermi surface map for the TB bands 2H-TaSe2 1T-TaS2

  38. Spectral Function for 2H-TaSe2 After DMFT Before DMFT

  39. Evolution of Spectral Function and fitting ARPES

  40. Conductivity and resistivity from DMFT

  41. DMFT with inter-orbital hopping for 2H-TaSe2

  42. Opening of gap with increase in temperature

  43. Pressure dependence of Fermi Surface

  44. Change in spectral function with pressure

  45. Temperature dependent Spectral function at different pressure

  46. Change in resistivity at different pressure

  47. Conclusion • DMFT Spectral function is broadened. • With application of Inter-orbital coulomb interaction the system goes to insulator. • With application of Inter-orbital hopping DMFT orbital occupation changes from LDA. • There is a opening of gap with increasing temperature up-to 140K. • With decreasing pressure hole pockets in the Fermi surface disappear. • With increasing pressure the gap formed at the Fermi surface decreases.

  48. Thank You

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