Higher-Order Topological Instanton Tunneling Oscillation

TL;DR

This paper introduces a novel instanton interference effect in 2D higher-order topological insulators, leading to gate-tunable energy oscillations of corner states, which can be experimentally observed to identify such materials.

Contribution

It proposes a new topological tunneling interference effect involving instanton pairs in higher-order topological insulators, with potential experimental detection.

Findings

Energy splitting oscillates with gate voltage.

Oscillatory nodes indicate tunneling suppression.

Twisted bilayer graphene as a candidate material.

Abstract

We propose a new type of instanton interference effect in two-dimensional higher-order topological insulators. The intercorner tunneling consists of the instanton and the anti-instanton pairs that travel through the boundary of the higher-order topological insulator. The Berry phase difference between the instanton pairs causes the interference of the tunneling. This topological effect leads to the gate-tunable oscillation of the energy splitting between the corner states, where the oscillatory nodes signal the perfect suppression of the tunneling. We suggest this phenomenon as a unique feature of the topological corner states that differentiate from trivial bound states. In the view of experimental realization, we exemplify twisted bilayer graphene, as a promising candidate of a two-dimensional higher-order topological insulator. The oscillation can be readily observed through the transport experiment that we propose. Thus, our work provides a feasible route to identify higher-order topological materials.