Quantum disordered phase near the Mott transition in the staggered-flux Hubbard model on a square lattice

TL;DR

This study explores the ground state phases of the staggered-flux Hubbard model on a square lattice, revealing a non-magnetic intermediate phase with gapless spin excitations that may be an algebraic spin liquid.

Contribution

It identifies a novel intermediate correlated insulator phase with no magnetic or dimer order, characterized by gapless spin excitations, near the Mott transition in the model.

Findings

System is semi-metal for U/t less than ~5.6.

System becomes a Mott insulator with antiferromagnetic order for U/t greater than ~6.6.

Intermediate phase exhibits gapless spin excitations and power-law spin correlations.

Abstract

We investigate ground state properties of the half-filled staggered-flux Hubbard model on a square lattice. Energy gaps to charge and spin excitations and magnetic as well as dimer orders are calculated as a function of interaction strength $U/t$ by means of constrained-path quantum Monte Carlo method. It is found that the system is a semi-metal at $U/t\lesssim 5.6$ and a Mott insulator with long-range antiferromagnetic order at $U/t \gtrsim 6.6$. In the range $5.6\lesssim U/t\lesssim 6.6$, the ground state is an correlated insulator where both magnetic and dimer orders are absent. Furthermore, spin excitation in the intermediate phase appears to be gapless, and the measured spin-spin correlation function exhibits power-law decaying behavior. The data suggest that the non-magnetic ground state is a possible candidate for the putative algebraic spin liquid.