Quantum Melting of Charge Order due to Frustration in Two-Dimensional Quarter-Filled Systems

TL;DR

This study reveals that geometrical frustration in two-dimensional quarter-filled systems can induce a robust quantum melting of charge order, leading to a metallic phase even at strong Coulomb interactions.

Contribution

It demonstrates that frustration can stabilize a metallic phase in a 2D quarter-filled extended Hubbard model, a novel insight into charge order suppression.

Findings

Frustration induces a broad metallic phase at V' ~ V.

Quantum melting of charge order is robust against lattice modifications.

Charge ordered states are destabilized by geometrical frustration.

Abstract

The effect of geometrical frustration in a two-dimensional 1/4-filled strongly correlated electron system is studied theoretically, motivated by layered organic molecular crystals. An extended Hubbard model on the square lattice is considered, with competing nearest neighbor Coulomb interaction, V, and that of next-nearest neighbor along one of the diagonals, V', which favor different charge ordered states. Based on exact diagonalization calculations, we find a metallic phase stabilized over a broad window at V' ~ V even for large Coulomb repulsion strengths as a result of frustrating the charge ordered states. Slightly modifying the lattice geometry relevant to the actual organic compounds does not alter the results, suggesting that this `quantum melting' of charge order is a robust feature of frustrated strongly correlated 1/4-filled systems.