Quantum Transport Properties of an Exciton Insulator/Superconductor Hybrid Junction

Abstract

A theoretical study of electronic transport in a hybrid junction consisting of an excitonic insulator sandwiched between a normal and a superconducting electrode is presented. The normal region is described as a two‐band semi‐metal 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 Γ in the quasi‐particle spectrum. Four different scattering processes at both interfaces are identified: 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. The differential conductance of the structure is calculated and the existence of a minimum at voltages of the order of the excitonic gap is shown. The findings are useful toward the detection of the excitonic condensate and provide a plausible explanation for recent transport experiments on HgTe quantum wells and InAs/GaSb bilayer systems.