Josephson radiation from nonlinear dynamics of Majorana zero modes

TL;DR

This paper models the nonlinear dynamics of Majorana zero modes in topological Josephson junctions to explain experimental Josephson radiation observations, predicting new spectral features and resolving previous theoretical-experimental discrepancies.

Contribution

It introduces a nonlinear dynamical model for Majorana modes in Josephson junctions, aligning theory with experimental radiation spectra and predicting novel spectral phenomena.

Findings

Quantitative agreement with experimental Josephson radiation spectra

Prediction of an interrupted emission line in the spectrum

Identification of a chaotic regime in the radiation spectrum

Abstract

Josephson radiation is a powerful method to probe Majorana zero modes in topological superconductors. Recently, Josephson radiation with half the Josephson frequency has been experimentally observed in a HgTe-based junction, possibly from Majorana zero modes. However, this radiation vanishes above a critical voltage, sharply contradicting previous theoretical results. In this work, we theoretically obtain a radiation spectrum quantitatively in agreement with the experiment after including the nonlinear dynamics of the Majorana states into the standard resistively shunted junction model. We further predict two new structures of the radiation spectrum for future experimental verification: an interrupted emission line and a chaotic regime. We develop a fixed-point analysis to understand all these features. Our results resolve an apparent discrepancy between theory and experiments, and will inspire reexamination of structures in radiation spectra of various topological Josephson junctions.