Jordan-Wigner fermionization of quantum spin systems on arbitrary 2D lattices: A mutual Chern-Simons approach

TL;DR

This paper introduces a mutual Chern-Simons gauge theory approach for fermionizing quantum spin systems on arbitrary 2D lattices, enabling analysis of complex topological phases and excitations.

Contribution

It develops a novel mutual Chern-Simons framework that incorporates dual lattice gauge fields, allowing consistent fermionization on arbitrary 2D lattices and application to the Kitaev model.

Findings

Topological phase degradation explained by the theory.

Effective one-dimensional behavior of low-energy excitations.

Validation through spin-wave calculations.

Abstract

A variety of analytical approaches have been developed for the study of quantum spin systems in two dimensions, the notable ones being spin-waves, slave boson/fermion parton constructions, and for lattices with one-to-one local correspondence of faces and vertices, the 2D Jordan-Wigner (JW) fermionization. Field-theoretically, JW fermionization is implemented through Chern-Simons (CS) flux attachment. For a correct fermionization of lattice quantum spin-$1/2$ magnets, it is necessary that the fermions obey mutual bosonic (anyonic) statistics under exchange - this is not possible to implement on arbitrary 2D lattices if fermionic matter couples only to the lattice gauge fields. Enlarging the gauge degrees of freedom to include the dual lattice allows the construction of consistent mutual Chern-Simons field theories. Here we propose a mutual CS theory where the microscopic (spin) degrees of freedom are represented as lattice fermionic matter additionally coupled to specific combinations of dual lattice gauge fields that depend on the local geometry. We illustrate the use of this method for understanding the properties of a honeycomb Kitaev model subjected to a strong Zeeman field in the $z$-direction. Our CS gauge theory framework provides an understanding why the topological phase is degraded at lower (higher) critical fields for the ferro- (antiferro-) magnetic Kitaev interaction. Additionally, we observe an effectively one-dimensional character of the low-excitations at higher fields in the $z$-direction which we also confirm by spin-wave calculations.