Probing quasiparticle excitations in a hybrid single electron transistor

TL;DR

This paper studies quasiparticle behavior in a hybrid single electron transistor to enhance its use as a precise current source, revealing how device operation and environment excite quasiparticles and how they relax into traps.

Contribution

It provides direct measurements of quasiparticle densities, compares trap geometries, and models quasiparticle dynamics quantitatively.

Findings

Quasiparticle densities below 3 μm^-3 at 20 MHz.

Quasiparticles are excited by device operation and electromagnetic environment.

Modeling with sequential tunneling and diffusion explains the observations.

Abstract

We investigate the behavior of quasiparticles in a hybrid electron turnstile with the aim of improving its performance as a metrological current source. The device is used to directly probe the density of quasiparticles and monitor their relaxation into normal metal traps. We compare different trap geometries and reach quasiparticle densities below 3um^-3 for pumping frequencies of 20 MHz. Our data show that quasiparticles are excited both by the device operation itself and by the electromagnetic environment of the sample. Our observations can be modelled on a quantitative level with a sequential tunneling model and a simple diffusion equation.