FLEX Study of ’-(ET)2AuCl2

Hiori Kino (National institute for materias science)Hiroshi Kontani (Nagoya Univ.)

Tsuyoshi Miyazaki (National institute for materials science)

Motivation

’-(ET)2ICl2 ’-(ET)2AuCl2*

Structure

ambient pressure

under applied pressure

--- Almost the same ET stacking---

AF insulator insulator

superconductivity insulator

Why?*Taniguchi, et al., JPSJ 74, 1370 (2005).

Dimensionality of Fermi surfaces

Quasi-1D Quasi-1D

Electronic structure (first-principles study by Miyazaki et al,)

’-(ET)2ICl2 ’-(ET)2AuCl2

Ambient pressure

Applied pressure 3D2D

0GPa 4GPa 8GPa

12GPa 16GPa 20GPa

Fermi surfaces (tight binding fit)

a*

c*

b*

Q?

higher dimensionality of Fermi surface stabilize AF phase in ’-(ET)2AuCl2?

Methods:Hamiltonian:•tight binding model (ET dimer model) •effective on-site (intra-dimer) Coulomb interaction

Perturbation theory:•FLEX-approximation

nnUcctH effjiij

Results

TN

No SC phase

Ueff=0.5eV

Discussion

AF

SC Pressure

Tem

pera

t ure

’-(ET)2ICl2

Suppress(→1D)

2D

Pressure

Tem

pera

ture

AF

’-(ET)2AuCl2

Enhance(2D→3D)Suppress

(→1D)No SC phase

Fermi surface nesting?U?

a*

c*

b*

TN

intralayerdimensionality

tem

pera

ture

TN

TSC

interlayer

dimensionality

Discussion (2)

TN

PressureAuCl2

PressureICl2

Fermi surfaces (extended zone)

12GPa 20GPa

Summary

’-(ET)2AuCl2

AF phase is stabilized under applied pressures.

Reason:Higher-dimensionalityU → better FS nesting

Fermi surfaces (2D, b-axis-off)

0GPa 4GPa 8Gpa

12GPa 16GPa 20GPa

a*

c*

→Destabilize AF?