Solitons with irrational charge in a one-dimensional quantum ferroelectric

TL;DR

This paper investigates a one-dimensional electron-phonon system revealing three insulating phases and discovers soliton excitations with irrational charge and low effective mass, using mean-field and DMRG methods.

Contribution

It introduces the existence of irrational charge solitons in a 1D ferroelectric phase, a novel finding in electron-phonon models.

Findings

Identification of three distinct insulating phases.

Discovery of solitons with irrational charge.

Solitons have a surprisingly light effective mass.

Abstract

We use analytic (mean-field) and density-matrix renormalization group (DMRG) methods to study a simplified one-dimensional version of the SSH-Holstein model of electron-phonon interactions with one electron per site (half filling) where, as a function of the ratio of the two couplings, three distinct insulating phases arise - a site-centered charge-density-wave (CDW), a bond-centered bond-density-wave (BDW), and an intermediate ferroelectric (inversion-symmetry breaking) phase with coexisting CDW and BDW order. In the intermediate phase our DMRG results establish the existence of point-like soliton excitations with irrational charge (that depends on a ratio of coupling constants) and either spin 1/2 or spin 0, and a surprisingly light effective mass.