Possibility of Gapless Spin Liquid State by One-Dimensionalization

Abstract

Motivated by the observation of a gapless spin liquid state in κ-(BEDT-TTF)₂Cu₂(CN)₃, we analyze the anisotropic triangular lattice S=1⁄2 Heisenberg model with the resonating valence bond mean-field approximation. Paying attention to the small quasi-one-dimensional anisotropy of the material, we take an approach from one-dimensional (1D) chains coupled with frustrating zigzag bonds. By calculating one-particle excitation spectra changing anisotropy parameter J′⁄J from the decoupled 1D chains to the isotropic triangular lattice, we find almost gapless excitations in the wide range from the 1D limit. This one-dimensionalization by frustration is considered to be a candidate for the mechanism of the gapless spin liquid state.