the “normal” state of layered dichalcogenides
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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. - PowerPoint PPT PresentationTRANSCRIPT
The “normal” state of layered dichalcogenides
Arghya Taraphder
Indian Institute of Technology Kharagpur
Department of Physics and Centre for Theoretical Studies
Workshop @ Harish Chandra Research Institute, November 12-14, 2010
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)
Dichalcogenides: crystal structure
Glossary
Typical Phase diagram
D.B. Mcwhan, et al. PRL 45,269(1980)(2H-TaSe2)
A. F. Kusmartseva, et al. PRL 103, 236401(2009) (1T-TiSe2)
B. Sipos, et al. Nat. mater. 7, 960 (2008) (IT-TaS2)
2H-TaSe2
1T-T
iSe2
1T-TaS2
2H-TaS2Cava et al.
Phase diagram of 1T-TiSe2 : doping and pressure
Quantum critical?
Castro-Neto, loc cit
Cava, PRL (2008)
DC Resistivities
Aebi, loc cit
Resistivity of TMDs: 1T and 2H
Y. Ueda, et al. Journal of Physical Societyof Japan 56 2471-2476, (1987).
P. Aebi, et al. Journal of Electron Spectroscopy and Related Phenomena117–118 (2001)
Vescoli et al, PRL 81, 453 (1998)
2H-TaSe2
Op
tica
l co
nd
uct
ivit
y(0
.04
< E
< 5
eV
ran
ge)
R C
Dyn
es,
et a
l.,
EP
JB 3
3, 1
5 (
200
3)
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)
Dynes loc cit
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
Transport scattering rateab-plane
Tra
nsp
ort
sca
tter
ing
rat
ec-
axis
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
“QP” Scattering Rate & SE from ARPES
Valla, PRL 85, 4759 (2000)
Valla, loc. cit..Fit with momentum-indep. SE
Aebi, JES 117, 433 (2001)
Electronic structure
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
2H-TaSe2
H.E. Brauer,et al. J. Phys. Cond. Matter 13, 9879 (2001)
Band structure
Aebi, JES 117, 433 (2001)
Tight Binding Description
N V Smith, et al. J. Phys. C:Solid State Phys. 18 (1985) 3175-3189
Tight binding fit near FL for 2H-TaSe2
N V Smith, et al. J. Phys. C:Solid State Phys. 18 (1985) 3175-3189.
Fermi surface map for the TB bands
2H-TaSe2 1T-TaS2
ARPES - 2H-TaSe2
Liu
, P
RL
80
, 57
62
(199
8)
Liu
, P
RL
80
, 57
62
(199
8)
Valla et al, PRL 85, 4759 (2000)
CDW Gap ? Castro_Neto, PRL 86, 4382 (2001)
)Pseudogap in 2H-TaSe2, Borisenko et al, PRL 100, 196402 (2008)
Fermi surface and ARPES - 2H type
N V Smith, et al. J. Phys. C: Solid State Phys. 18 (1985) 3175-3189.
S V Borisenko, et al.Phys. Rev. Lett. 100, 196402 (2008)
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)
Fermi surface of 1T-TiSe2
P. Aebi, et al. Phys.Rev.B 61 16213, (2000)
Superlattice & BZ in the CDW phaseof Dichalcogenides
N V Smith, et al. J. Phys. C:Solid State Phys. 18 (1985) 3175-3189.
2H-TaSe2
1T-TaS2
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.
Fermi surface map for the TB bands
2H-TaSe2 1T-TaS2
Spectral Function for 2H-TaSe2
Before DMFT After DMFT
Evolution of Spectral Function and fitting ARPES
Conductivity and resistivity from DMFT
DMFT with inter-orbital hopping for 2H-TaSe2
Opening of gap with increase in temperature
Pressure dependence of Fermi Surface
Change in spectral function with pressure
Temperature dependent Spectral function at different pressure
Change in resistivity at different pressure
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.