Spectral features of voltage pulses in interacting helical channels

Matteo Acciai,Alessio Calzona,Maura Sassetti,Matteo Carrega,E Puppin

doi:10.1051/epjconf/202023000009

Abstract

We investigate the interplay of voltage-driven excitations and electron-electron interactions in a pair of counterpropagating helical channels capacitively coupled to a time-dependent gate. By focusing on the non-equilibrium spectral properties of the system, we show how the spectral function is modified by external drives with different time profile in presence of Coulomb interactions. In particular, we focus on a Lorentzian drive and a square single pulse. In presence of strong enough electron-electron interactions, we find that both drives can result in minimal excitations, i.e. characterized by an excess spectral function with a definite sign. This is in contrast with what happens in the non-interacting case, where only properly quantized Lorentzian pulses are able to produce minimal excitations.

Highlights

The ability to control electronic transport more and more precisely, together with the advances in nanofabrication techniques, has allowed the development of the research field known as electron quantum optics (EQO) [1, 2]
We considered the effects of single voltage pulses applied to a top gate, capacitively coupled with two helical channels
Such a quantity allows to discriminate between minimal excitations, featuring a spectral function with definite sign, and non-minimal ones, featuring sign changes in their spectral functions

Summary

Introduction

The ability to control electronic transport more and more precisely, together with the advances in nanofabrication techniques, has allowed the development of the research field known as electron quantum optics (EQO) [1, 2]. We address this problem by considering the non-equilibrium spectral properties of a pair of interacting helical channels, coupled to an external drive, and show that they exhibit peculiar features compared to the non-interacting case. While it is well known that properly quantized Lorentzian pulses [19,20,21,22] provide the only way to generate minimal excitations in a noninteracting one-dimensional channel, we show that this is no longer the case if interactions are present. As far as the particle density is concerned, the voltage pulse generates excitations propagating both to the right (x > 0) and to the left (x < 0) with respect to the injection point x = 0. This is because in this case a right-moving spin-down excitation does not exist, due to the fact that in a non-interacting helical system right-moving excitations can only have spin-up component

Non-equilibrium spectral function

General properties

Lorentzian pulses

Square pulses

Conclusions