# Interacting topological edge channels

## TL;DR

This paper investigates interactions between topological edge channels in a quantum spin Hall insulator, revealing a new conductance plateau at e^2/h explained by electron interactions, with implications for quantum optics and Majorana fermions.

## Contribution

It demonstrates the interaction effects between edge states in a quantum spin Hall insulator using a topological quantum point contact, revealing a novel conductance plateau at e^2/h.

## Key findings

- Observation of a new conductance plateau at e^2/h
- Band structure and interaction effects explain the plateau
- Implications for quantum optics and Majorana fermions

## Abstract

Electrical currents in a quantum spin Hall insulator are confined to the boundary of the system. The charge carriers can be described as massless relativistic particles, whose spin and momentum are coupled to each other. While the helical character of those states is by now well established experimentally, it is a fundamental open question how those edge states interact with each other when brought in spatial proximity. We employ a topological quantum point contact to guide edge channels from opposite sides into a quasi-one-dimensional constriction, based on inverted HgTe quantum wells. Apart from the expected quantization in integer steps of $2 e^2/h$, we find a surprising additional plateau at $e^2/h$. We explain our observation by combining band structure calculations and repulsive electron-electron interaction effects captured within the Tomonaga-Luttinger liquid model. The present results may have direct implications for the study of one-dimensional helical electron quantum optics, Majorana- and potentially para-fermions.