Interfacial Fermi Loops from Interfacial Symmetries

TL;DR

This paper introduces the concept of interfacial symmetries, leading to novel interface state dispersions such as Fermi loops, demonstrated through a tight-binding model, revealing new topological features at interfaces.

Contribution

It proposes interfacial symmetries like particle-hole and time-reversal symmetry, and shows their role in creating Fermi loops at interfaces, a novel topological phenomenon.

Findings

Interfacial particle-hole symmetry leads to Fermi loops at interfaces.

Fermi loops originate from Pfaffian sign changes in the Hamiltonian.

Numerical demonstration using Fu-Kane-Mele model confirms the theoretical predictions.

Abstract

We propose a concept of interfacial symmetries such as interfacial particle-hole symmetry and interfacial time-reversal symmetry, which appear in interfaces between two regions related to each other by particle-hole or time-reversal transformations. These symmetries result in novel dispersion of interface states. In particular for the interfacial particle-hole symmetry the gap closes along a loop ("Fermi loop") at the interface. We numerically demonstrate this for the Fu-Kane-Mele tight-binding model. We show that the Fermi loop originates from a sign change of a Pfaffian of a product between the Hamiltonian and a constant matrix.