Heat-mode excitation in a proximity superconductor

TL;DR

This study demonstrates heat-mode excitation in a superconductor-based nanowire device by using shot noise measurements to analyze heat transport and its tunability, revealing new insights into charge-neutral quasiparticle modes.

Contribution

It introduces a novel experimental approach to probe heat modes in mesoscopic superconductors via shot noise, expanding understanding beyond charge transport measurements.

Findings

Heat-mode transport characterized with thermal conductance ~ e^2/h.

Heat guiding along the superconductor interface observed and tunable by gate voltage.

Signatures of heat-mode detected in non-local charge transport measurements.

Abstract

Mesoscopic superconductivity deals with various quasiparticle excitation modes, only one of them -- the charge-mode -- being directly accessible for conductance measurements due to the imbalance in populations of quasi-electron and quasihole excitation branches. Other modes carrying heat or even spin, valley etc. currents populate the branches equally and are charge-neutral, which makes them much harder to control. This noticeable gap in the experimental studies of mesoscopic non-equilibrium superconductivity can be filled by going beyond the conventional DC transport measurements and exploiting spontaneous current fluctuations. Here, we perform such an experiment and investigate the transport of heat in an open hybrid device based on a superconductor proximitized InAs nanowire. Using shot noise measurements, we investigate sub-gap Andreev heat guiding along the superconducting interface and fully characterize it in terms of the thermal conductance on the order of $G_\mathrm{th}\sim e^2/h$, tunable by a back gate voltage. Understanding of the heat-mode also uncovers its implicit signatures in the non-local charge transport. Our experiments open a direct pathway to probe generic charge-neutral excitations in superconducting hybrids.