Zero temperature Phase Diagram of Two Dimensional Hubbard Model

							Zero-temperature Phase Diagram of Two Dimensional Hubbard Model
K. Inabaa , A. Kogab , S. Sugaa , and N. Kawakamib
a
    Department of Applied Physics, Osaka University, Suita, Osaka 565-0871, Japan
b
    Department of Physics, Kyoto University, Kyoto 606-8502, Japan
Geometrical frustration has been one of the most active topics in the field of strongly correlated elec-
tron systems. In particular, recent experiments on the triangular lattice organic material κ-(BEDT-
TTF)2 Cu2 (CN)3 have attracted much interest. According to an NMR experiment, the Mott insulating
material κ-(ET)2 Cu2 (CN)3 does not exhibit any magnetic transition down to a quite low temperature
T ∼32mK. It suggests that the geometrical frustration reveals a novel spin-liquid insulating state. Stimu-
lated by the experimental finding, theoretical studies for the Hubbard model on an anisotropic triangular
have been done by various methods1 . However, there is no consensus whether the non-magnetic insulating
state is stable or not, and thus complemental discussions are desired. Motivated by this, we investigate
the Hubbard model on the anisotropic triangular lattice, by the self-energy functional approach (SFA).
The SFA provides us an efficient and tractable way to deal with Mott transitions. In this study, we take
into account two types of AF order, (i) (π, π)-AF order and (ii) 120◦ -AF order. We obtain the phase
diagram of the model which is consistent with previous work. We find that a 120◦ -AF order is dominant
for t /t ≥ 0.8. In addition, we discuss whether the non-magnetic insulating phase is stable or not.
1
 B.Kyung and A.S.Tremblay, Phys. Rev. Lett. 97, 046402 (2006); T. Mizusaki and M. Imada, Phys.
Rev. B 74, 014421 (2006);T. Watanabe et. al., arXiv/0711.1702.