Conductance enhancement in quantum point contact-semiconductor-superconductor devices

TL;DR

This paper numerically investigates conductance in quantum point contact-superconductor devices, revealing conditions under which the expected conductance enhancement is suppressed, aligning with experimental observations.

Contribution

It demonstrates how quantum point contact modes and interface barriers influence conductance enhancement, providing insights into discrepancies between theory and experiments.

Findings

Conductance enhancement can be suppressed with few propagating modes.

Fermi level position significantly affects conductance behavior.

Interface barriers cause anomalous quasiparticle interference effects.

Abstract

We present numerical calculations of the conductance of an interface between a phase-coherent two-dimensional electron gas and a superconductor with a quantum point contact in the normal region. Using a scattering matrix approach we reconsider the geometry of De Raedt, Michielsen, and Klapwijk [Phys. Rev. B, 50, 631 (1994)] which was studied within the time-dependent Bogoliubov-de Gennes formalism. We find that the factor-of-two enhancement of the conductance G_NS compared to the normal state conductance G_N for ideal interfaces may be suppressed for interfaces with a quantum point contact with only a few propagating modes. The suppression is found to depend strongly on the position of the Fermi level. We also study the suppression due to a barrier at the interface and find an anomalous behavior caused by quasiparticle interference. Finally, we consider the limit of sequential tunneling and find a suppression of the factor-of-two enhancement which may explain the absence of conductance enhancement in experiments on metal-superconductor structures.