# Volkov-Pankratov states in topological heterojunctions

## TL;DR

This paper investigates the existence and properties of multiple surface states, including massless and massive ones, at smooth interfaces between topological insulators with opposite Z2 indices, highlighting their relativistic nature and experimental relevance.

## Contribution

It reveals the presence of massive Dirac surface states in topological heterojunctions, which are sensitive to interface smoothness and have implications for experiments.

## Key findings

- Massless surface state is non-degenerate and chiral.
- Massive surface states appear for sufficiently smooth interfaces.
- Surface states exhibit relativistic Landau band characteristics.

## Abstract

We show that a smooth interface between two insulators of opposite topological Z2 indices possesses multiple surface states, both massless and massive. While the massless surface state is non-degenerate, chiral and insensitive to the interface potential, the massive surface states only appear for a sufficiently smooth heterojunction. The surface states are particle-hole symmetric and a voltage drop reveals their intrinsic relativistic nature, similarly to Landau bands of Dirac electrons in a magnetic field. We discuss the relevance of the massive Dirac surface states in recent ARPES and transport experiments.