TY - JOUR

T1 - Pairing symmetries in a Hubbard model on an anisotropic triangular lattice

AU - Watanabe, Tsutomu

AU - Yokoyama, Hisatoshi

AU - Tanaka, Yukio

AU - Inoue, Jun ichiro

N1 - Funding Information:
This work is partly supported by Grant-in-Aids from the Ministry of Education, etc. Japan, from the Supercomputer Center, ISSP, Univ. of Tokyo, from NAREGI Nanoscience Project and for the 21st Century COE “Frontiers of Computational Science”.

PY - 2007/10/1

Y1 - 2007/10/1

N2 - To consider the paring symmetry formed in organic compounds κ-(BEDT-TTF)2X, we study the half-filled-band Hubbard model on an anisotropic triangular lattice (t in two bond directions and t′ in the other), using an optimization VMC method. As trial states, we adopt a coexisting state of an antiferromagnetic (AF) order and the dx2 - y2-wave RVB gap, in addition to the d + id- and d + d-wave gap states. In these states, we take account of the effect of band (or Fermi surface) renormalization. Magnetic Mott transitions occur, and a regime of robust superconductivity could not be found, in contrast with our previous study. In the insulating regime, the coexisting state in which an AF order prevails is always the lowest-energy state up to remarkably large t′/t (≲1.3), whereas a dxy-wave RVB state becomes predominant when t′/t exceeds this value. In the insulating regime, the effective Fermi surface, determined by the renormalized value over(t, ̃)′ / t, is markedly renormalized into different directions according to t′/t; for t′/t ≲ 1.3, it approaches that of the square lattice (over(t, ̃)′ / t = 0), whereas for t′/t ≳ 1.3, it becomes almost one-dimensional (over(t, ̃)′ / t ≫ 1).

AB - To consider the paring symmetry formed in organic compounds κ-(BEDT-TTF)2X, we study the half-filled-band Hubbard model on an anisotropic triangular lattice (t in two bond directions and t′ in the other), using an optimization VMC method. As trial states, we adopt a coexisting state of an antiferromagnetic (AF) order and the dx2 - y2-wave RVB gap, in addition to the d + id- and d + d-wave gap states. In these states, we take account of the effect of band (or Fermi surface) renormalization. Magnetic Mott transitions occur, and a regime of robust superconductivity could not be found, in contrast with our previous study. In the insulating regime, the coexisting state in which an AF order prevails is always the lowest-energy state up to remarkably large t′/t (≲1.3), whereas a dxy-wave RVB state becomes predominant when t′/t exceeds this value. In the insulating regime, the effective Fermi surface, determined by the renormalized value over(t, ̃)′ / t, is markedly renormalized into different directions according to t′/t; for t′/t ≲ 1.3, it approaches that of the square lattice (over(t, ̃)′ / t = 0), whereas for t′/t ≳ 1.3, it becomes almost one-dimensional (over(t, ̃)′ / t ≫ 1).

KW - Anisotropic triangular lattice

KW - Hubbard model

KW - Mott transition

KW - Pairing symmetry

KW - Variational Monte Carlo method

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U2 - 10.1016/j.physc.2006.12.027

DO - 10.1016/j.physc.2006.12.027

M3 - Article

AN - SCOPUS:34548479300

SN - 0921-4534

VL - 463-465

SP - 152

EP - 156

JO - Physica C: Superconductivity and its Applications

JF - Physica C: Superconductivity and its Applications

IS - SUPPL.

ER -