Fractionalization in a square-lattice model with time-reversal symmetry

TL;DR

This paper introduces a 2D time-reversal invariant square lattice model where topological defects in electron hopping lead to fractional charges, supported by analytical and numerical evidence.

Contribution

It presents a novel non-interacting electron model exhibiting fractional charges and analyzes their properties and potential realizations.

Findings

Fractional charges of e/2 are realized at vortex-like defects.

Charge fractionalization is confirmed by analytical and numerical methods.

The model preserves time-reversal symmetry and suggests possible experimental realizations.

Abstract

We propose a two-dimensional time-reversal invariant system of essentially non-interacting electrons on a square lattice that exhibits configurations with fractional charges e/2. These are vortex-like topological defects in the dimerization order parameter describing spatial modulation in the electron hopping amplitudes. Charge fractionalization is established by a simple counting argument, analytical calculation within the effective low-energy theory, and by an exact numerical diagonalization of the lattice Hamiltonian. We comment on the exchange statistics of fractional charges and possible realizations of the system.