Spectroscopic Signatures of Gate-Controlled Superconducting Phases

TL;DR

This paper explores how electrostatic gating influences tunneling conductance in superconductor heterostructures, revealing signatures of gate-controlled superconducting phases and distinguishing quantum effects from thermal influences.

Contribution

It provides the first detailed analysis of spectroscopic signatures of gate-induced superconducting phase modifications in SIN and SIS heterostructures.

Findings

Gate voltage increases quasiparticles in the superconducting gap.

SIN conductance peaks shift depending on surface interactions and gating.

SIS conductance features are asymmetric and broadened under gating.

Abstract

We investigate the tunneling conductance of superconductor-insulator-normal metal (SIN) and superconductor-insulator-superconductor (SIS) heterostructures with one superconducting side of the junction that is electrically driven and can exhibit $\pi$-pairing through a modification of the surface inversion asymmetric couplings. In SIN tunneling we find that the variation of the electrically driven interactions generally brings an increase of quasi-particles in the gap due to orbitally polarized depaired states, irrespective of the inter-band phase rearrangement. The peak of SIN conductance at the gap edge varies with a trend that depends both on the strength of the surface interactions as well as on the character of the gate-induced superconducting state. While this shift can be also associated with thermal effects in the SIN configuration, for the SIS geometry at low temperature the electric field does not yield the characteristic matching peak at voltages related with the difference between the gaps of the superconducting electrodes. This observation sets out a distinctive mark for spectroscopically distinguishing the thermal population effects from the quantum gate-driven signatures. In SIS the electrostatic gating yields a variety of features with asymmetric peaks and broadening of the conductance spectral weight. These findings indicate general qualitative trends for both SIN and SIS tunneling spectroscopy which could serve to evaluate the impact of gate-control on superconductors and the occurrence of non-centrosymmetric orbital antiphase pairing.