Current switching behavior mediated via hinge modes in higher-order topological phases using altermagnets

TL;DR

This paper presents a theoretical framework for engineering higher-order topological phases in 3D topological insulators using d-wave altermagnets, enabling controllable hinge modes and current switching.

Contribution

It introduces a novel approach to induce and control higher-order topological phases and hinge modes via altermagnetic coupling in topological insulators.

Findings

Hybrid-order topological phase with coexisting first- and second-order phases.

Distinct hinge modes in second-order topological insulators.

Tunable hinge mode propagation enabling current switching.

Abstract

We propose a theoretical framework to engineer hybrid-order and higher-order topological phases in three-dimensional topological insulators by coupling to $d$-wave altermagnets (AMs). Presence of only $d_{x^2-y^2}$-type AM drives the system into a hybrid-order topological phase where both first-order and second-order topological phases coexist. This phase is characterized by spectral analysis, low-energy surface theory, dipolar and quadrupolar winding numbers, and it's signature is further confirmed by two-terminal differential conductance calculations. Incorporation of the $d_{x^2-z^2}$-type AM drives the system into two second-order topological insulator phases hosting distinct type of hinge modes. These two variants of second-order topological phases are also topologically characterized by spectral analysis, topological invariants, low-energy surface thoery, and transport calculations. Importantly, the localization and direction of propagation of these one-dimensional hinge modes are controllable by tuning the relative strengths of the alermagnetic exchange orders. We utilize this feature to propose a tunable current-switching behaviour mediated via the hinge modes. Our results establish AMs based hybrid structure as a versatile platform for controllable higher-order topology and hinge-mediated device applications.