1. FLEX Study of  ’-(ET) 2 AuCl 2 Hiori Kino ( National institute for materias science ) Hiroshi Kontani ( Nagoya Univ. ) Tsuyoshi Miyazaki ( National institute for materials science )

2. Motivation  ’-(ET) 2 ICl 2  ’-(ET) 2 AuCl 2 * Structure ambient pressure under applied pressure --- Almost the same ET stacking--- AF insulator insulator superconductivityinsulator Why? *Taniguchi, et al., JPSJ 74, 1370 (2005).

3. Dimensionality of Fermi surfaces Quasi-1D Electronic structure (first-principles study by Miyazaki et al,)  ’-(ET) 2 ICl 2  ’-(ET) 2 AuCl 2 Ambient pressure Applied pressure 3D2D

4. 0GPa 4GPa 8GPa 12GPa16GPa20GPa Fermi surfaces ( tight binding fit ) a* c* b*

5. Q? higher dimensionality of Fermi surface stabilize AF phase in  ’-(ET) 2 AuCl 2 ? Methods: Hamiltonian: tight binding model (ET dimer model) effective on-site (intra-dimer) Coulomb interaction Perturbation theory: FLEX-approximation

6. Results TNTN No SC phase U eff =0.5eV

7. Discussion AF SC Pressure Temperature  ’-(ET) 2 ICl 2 Suppress (→1D) 2D Pressure Temperature AF  ’-(ET) 2 AuCl 2 Enhance (2D→3D) Suppress (→1D) No SC phase  Fermi surface nesting? U? a* c* b* TNTN

8. intralayer dimensionality temperature TNTN T SC interlayer dimensionality Discussion (2) TNTN Pressure AuCl2 Pressure ICl2

9. Fermi surfaces (extended zone) 12GPa 20GPa

10. Summary  ’-(ET) 2 AuCl 2 AF phase is stabilized under applied pressures. Reason: Higher-dimensionality U → better FS nesting

11. Fermi surfaces ( 2D, b-axis-off ) 0GPa4GPa8Gpa 12GPa16GPa 20GPa a* c* →Destabilize AF?