Order and disorder in the triangular-lattice t-J-V model at 2/3 electron density

TL;DR

This paper investigates the complex interplay of charge, magnetic, and phase orders in the triangular-lattice t-J-V model at 2/3 electron density, revealing robust charge order and various magnetic phases driven by hopping and interaction parameters.

Contribution

It introduces a detailed analysis of the t-J-V model at 2/3 electron density using series expansion and mean-field methods, highlighting novel charge and magnetic ordering phenomena.

Findings

Charge order is very robust for t<0.

Hopping to the third sublattice can enhance Neel order.

Nagaoka ferromagnetic state appears at large negative t and small V.

Abstract

Motivated by the recent discovery of superconductivity in Na$_x$CoO$_2\cdot y$H$_2$O, we use series expansion methods and cluster mean-field theory to study spontaneous charge order, Neel order, ferromagnetic order, dimer order and phase-separation in the triangular-lattice t-J-V model at 2/3 electron density. We find that for t<0, the charge ordered state, with electrons preferentially occupying a honeycomb lattice, is very robust. Quite surprisingly, hopping to the third sublattice can even enhance Neel order. At large negative t and small V, the Nagaoka ferromagnetic state is obtained. For large positive t, charge and Neel order vanish below a critical V, giving rise to an itinerant antiferromagnetically correlated state.