Period-doubling in the phase dynamics of a shunted HgTe quantum well Josephson junction

TL;DR

This study shows that period-doubling in a HgTe quantum well Josephson junction's phase dynamics, caused by nonlinear effects, can produce signals mimicking topological states, emphasizing careful interpretation of such phenomena.

Contribution

The paper demonstrates that nonlinear dynamics and spurious inductance in a HgTe quantum well Josephson junction can cause period-doubling and half-frequency emission, challenging interpretations of topological signatures.

Findings

Period-doubling leads to emission at half the Josephson frequency.

Nonlinear dynamics can be controlled via gate voltage, magnetic field, and temperature.

Model accurately reproduces experimental observations without topological assumptions.

Abstract

The fractional AC Josephson effect is a discerning property of topological superconductivity in hybrid Josephson junctions. Recent experimental observations of missing odd Shapiro steps and half Josephson frequency emission in various materials have sparked significant debate regarding their potential origin in the effect. In this study, we present microwave emission measurements on a resistively shunted Josephson junction based on a HgTe quantum well. We demonstrate that, with significant spurious inductance in the shunt wiring, the experiment operates in a nonlinear dynamic regime characterized by period-doubling. This leads to additional microwave emission peaks at half of the Josephson frequency, $f_J/2$, which can mimic the $4\pi$-periodicity of topological Andreev states. The observed current-voltage characteristics and emission spectra are well-described by a simple RCLSJ model. Furthermore, we show that the nonlinear dynamics of the junction can be controlled using gate voltage, magnetic field, and temperature, with our model accurately reproducing these effects without incorporating any topological attributes. Our observations urge caution in interpreting emission at $f_J/2$ as evidence for gapless Andreev bound states in topological junctions and suggest the appropriate parameter range for future experiments.