Quantum spin liquid with fermionized pi-vortices

TL;DR

This paper investigates quantum spin liquid states near the Mott transition in a 2D pi-flux Hubbard model, revealing a transition from a nodal spin liquid with fermionic excitations to a gapped Z2 topological spin liquid under anisotropy.

Contribution

It introduces a theoretical framework describing the transition between different quantum spin liquid states using mutual Chern-Simons theory.

Findings

Identification of a nodal spin liquid with fermionic excitations

Discovery of a Z2 topological spin liquid with gapped excitations under anisotropy

Development of a low-energy effective theory for these spin liquids

Abstract

In this paper, we study the non-magnetic insulator state near Mott transition of 2D pi-flux Hubbard model on square lattice and find that such non-magnetic insulator state is quantum spin liquid state with nodal fermionic excitations - nodal spin liquid (NSL). When there exists small easy-plane anisotropic energy, the ground state becomes Z2 topological spin liquid (TSL) with full gapped excitations. The U(1)times U(1) mutual--Chern-Simons (MCS) theory is obtained to describe the low energy physics of NSL and TSL.