Nonsymmorphic chiral symmetry and solitons in the Rice-Mele model

Allen, Rebecca and Gibbons, Holly and Sherlock, Alex and Stanfield, Harvey and McCann, Edward (2022) Nonsymmorphic chiral symmetry and solitons in the Rice-Mele model. Physical Review B: Condensed Matter and Materials Physics, 106 (16): 165409. ISSN 2469-9969

Text (cdw_authoraccepted2022_09_26)
cdw_authoraccepted2022_09_26.pdf - Accepted Version
Available under License Creative Commons Attribution.
Download (1MB)

Abstract

The Rice-Mele model has two topological and spatial-inversion-symmetric phases, namely, the Su-Schrieffer-Heeger (SSH) phase with alternating hopping only, and the charge-density-wave (CDW) phase with alternating energies only. The chiral symmetry of the SSH phase is robust in position space, so that it is preserved in the presence of the ends of a finite system and of textures in the alternating hopping. However, the chiral symmetry of the CDW phase is nonsymmorphic, resulting in a breaking of the bulk topology by an end or a texture in the alternating energies. We consider the presence of solitons (textures in position space separating two degenerate ground states) in finite systems with open boundary conditions. We identify the parameter range under which an atomically sharp soliton in the CDW phase supports a localized state which lies within the band gap, and we calculate the expectation value py of the nonsymmorphic chiral operator for this state, and the soliton electric charge. As the spatial extent of the soliton increases beyond the atomic limit, the energy level approaches zero exponentially quickly or in a manner inversely proportional to the width, depending on microscopic details of the soliton texture. In both cases, the difference of py from 1 is inversely proportional to the soliton width, while the charge is independent of the width. We investigate the robustness of the soliton level in the presence of disorder and sample-to-sample parameter variations, comparing it with a single soliton level in the SSH phase with an odd number of sites.