Quantum Transport Properties of an Exciton Insulator/Superconductor Hybrid Junction

TL;DR

This paper theoretically investigates electronic transport in a hybrid junction with an excitonic insulator between normal and superconducting electrodes, revealing unique scattering processes and conductance features that aid in detecting excitonic condensates.

Contribution

It introduces a detailed theoretical model of transport in exciton insulator/superconductor hybrids, identifying specific scattering processes and conductance signatures.

Findings

Existence of a conductance minimum at voltages near the excitonic gap

Identification of four scattering processes at interfaces

Explanation of recent experimental results in quantum well systems

Abstract

We present a theoretical study of electronic transport in a hybrid junction consisting of an excitonic insulator sandwiched between a normal and a superconducting electrode. The normal region is described as a two-band semimetal and the superconducting lead as a two-band superconductor. In the excitonic insulator region, the coupling between carriers in the two bands leads to an excitonic condensate and a gap $\Gamma$ in the quasiparticle spectrum. We identify four different scattering processes at both interfaces. Two types of normal reflection, intra- and inter-band; and two different Andreev reflections, one retro-reflective within the same band and one specular-reflective between the two bands. We calculate the differential conductance of the structure and show the existence of a minimum at voltages of the order of the excitonic gap. Our findings are useful towards the detection of the excitonic condensate and provide a plausible explanation of recent transport experiments on HgTe quantum wells and InAs/GaSb bilayer systems.