Floating Edge Bands in the Bernevig-Hughes-Zhang model with Altermagnetism

TL;DR

This paper demonstrates the emergence of floating edge bands in a modified Bernevig-Hughes-Zhang model with altermagnetism, revealing their topological properties and robustness, thus advancing understanding of topological phases in quantum materials.

Contribution

It introduces a simplified model with altermagnetism that exhibits floating edge bands, providing analytical insights and topological characterization of these states.

Findings

Floating edge bands appear in the modified BHZ model with altermagnetism.

Topological phase diagrams show strong and weak topological properties.

Floating edge bands are robust against various perturbations.

Abstract

Floating edge bands (FEB) have been identified in systems such as obstructed atomic insulators and layered nonsymmorphic semimetals, attracting considerable interest recently. Here we demonstrate that FEB can arise in a simplified model incorporating altermagnetism. By enhancing the Bernevig-Hughes-Zhang model on a square lattice with additional altermagnetic and Zeeman fields perpendicular to the 2D plane, we uncover the emergence of FEB that are distinct from the bulk bands across the entire Brillouin zone and over broad parameter regimes. We calculate topological phase diagrams, highlighting the strong topological properties characterized by the Chern number and the weak topological properties marked by the winding number. Furthermore, we provide analytical results of the energy spectrum and the wave functions of the FEB. We also study the robustness of the FEB, showcasing its resilience against various perturbations such as geometric rotation, energy spectrum asymmetry, and spin coupling. Our findings advance our understanding of FEB and may pave new avenues for further exploration of topological phases in quantum materials.