Phase Diagram of the Frustrated Square-Lattice Hubbard Model: Variational Cluster Approach

TL;DR

This study maps the phase diagram of the frustrated square-lattice Hubbard model at half filling, revealing various magnetic and nonmagnetic insulating phases influenced by quantum fluctuations and lattice geometry.

Contribution

It applies the variational cluster approximation to explore the phase diagram across different lattice geometries and identifies new nonmagnetic insulating phases due to frustration.

Findings

Identification of Neel, collinear, and spiral magnetic phases.

Discovery of a nonmagnetic insulating phase caused by quantum fluctuations.

Phase diagrams showing transitions between magnetic and nonmagnetic phases.

Abstract

The variational cluster approximation is used to study the frustrated Hubbard model at half filling defined on the two-dimensional square lattice with anisotropic next-nearest-neighbor hopping parameters. We calculate the ground-state phase diagrams of the model in a wide parameter space for a variety of lattice geometries, including square, crossed-square, and triangular lattices. We examine the Mott metal-insulator transition and show that, in the Mott insulating phase, magnetic phases with N\'eel, collinear, and spiral orders appear in relevant parameter regions, and in an intermediate region between these phases, a nonmagnetic insulating phase caused by the quantum fluctuations in the geometrically frustrated spin degrees of freedom emerges.