Magnetic Order and Mott Transition on the Checkerboard Lattice

TL;DR

This paper investigates the magnetic and electronic phases of the half-filled Hubbard model on the checkerboard lattice, revealing how virtual processes lift degeneracy, induce a flux-like Mott insulator, and lead to complex temperature-dependent crossovers and an insulator-metal transition.

Contribution

It demonstrates how virtual electronic processes generate multispin couplings that select a flux-like state in the Mott insulator, providing new insights into the interplay of frustration, correlations, and phase transitions.

Findings

Identification of a flux-like state in the Mott insulator.

Observation of a temperature-driven crossover to a 120-degree state.

Detection of a pseudogap near the insulator-metal transition.

Abstract

The checkerboard lattice, with alternating 'crossed' plaquettes, serves as the two dimensional analog of the pyrochlore lattice. The corner sharing plaquette structure leads to a hugely degenerate ground state, and no magnetic order, for classical spins with short range antiferromagnetic interaction. For the half-filled Hubbard model on this structure, however, we find that the Mott insulating phase involves virtual electronic processes that generate longer range and multispin couplings. These couplings lift the degeneracy, selecting a 'flux like' state in the Mott insulator. Increasing temperature leads, strangely, to a sharp crossover from this state to a '120 degree' correlated state and then a paramagnet. Decrease in the Hubbard repulsion drives the system towards an insulator-metal transition - the moments reduce, and a spin disordered state wins over the flux state. Near the insulator-metal transition the electron system displays a pseudogap extending over a large temperature window.