Nonlocal measurement of quasiparticle charge and energy relaxation in proximitized semiconductor nanowires using quantum dots

TL;DR

This study uses quantum dots as charge filters to measure quasiparticle charge and energy relaxation in superconducting-semiconducting nanowires, confirming their chargeless nature and complete relaxation processes.

Contribution

It introduces a nonlocal measurement technique employing quantum dots to directly probe quasiparticle charge and energy relaxation in hybrid nanowires.

Findings

Quasiparticles at the gap edge are chargeless.

Injected charge and energy fully relax in the nanowire.

Quantum dots effectively detect quasiparticle components.

Abstract

The lowest-energy excitations of superconductors do not carry an electric charge, as their wave function is equally electron-like and hole-like. This fundamental property is not easy to study in electrical measurements that rely on the charge to generate an observable signal. The ability of a quantum dot to act as a charge filter enables us to solve this problem and measure the quasiparticle charge in superconducting-semiconducting hybrid nanowire heterostructures. We report measurements on a three-terminal circuit, in which an injection lead excites a non-equilibrium quasiparticle distribution in the hybrid system, and the electron or hole component of the resulting quasiparticles is detected using a quantum dot as a tunable charge and energy filter. The results verify the chargeless nature of the quasiparticles at the gap edge and reveal the complete relaxation of injected charge and energy in a proximitized nanowire, resolving open questions in previous three-terminal experiments.