Predominant Magnetic States in Hubbard Model on Anisotropic Triangular Lattices

TL;DR

This study uses variational Monte Carlo to explore magnetic states in the Hubbard model on anisotropic triangular lattices, revealing how magnetic orders and metal-insulator transitions depend on interaction strength and lattice anisotropy.

Contribution

Introduces two new trial states with magnetic and singlet orderings, expanding understanding of magnetic phases and transitions in the Hubbard model on anisotropic lattices.

Findings

First-order metal-insulator transition occurs at smaller U/t with magnetic states.

F order persists up to t'/t.9 at high U/t.

120^\u00b0-AF order dominates for t'/t.9.

Abstract

Using an optimization variational Monte Carlo method, we study the half-filled-band Hubbard model on anisotropic triangular lattices, as a continuation of the preceding study [J. Phys. Soc. Jpn 75, 074707 (2006)]. We introduce two new trial states: (i) A coexisting state of (\pi,\pi)-antiferromagnetic (AF) and a d-wave singlet gaps, in which we allow for a band renormalization effect, and (ii) a state with an AF order of 120^\circ spin structure. In both states, a first-order metal-to-insulator transition occurs at smaller U/t than that of the pure d-wave state. In insulating regimes, magnetic orders always exist; an ordinary (\pi,\pi)-AF order survives up to t'/t\sim 0.9 (U/t=12), and a 120^\circ-AF order becomes dominant for t'/t \gsim 0.9. The regimes of the robust superconductor and of the nonmagnetic insulator the preceding study proposed give way to these magnetic domains.