# Zero-phase-difference Josephson current based on spontaneous symmetry-breaking via parametric excitation of a movable superconducting dot

## TL;DR

This paper introduces a novel nanoelectromechanical Josephson junction that exhibits supercurrent flow at zero phase difference due to spontaneous symmetry breaking, enabled by parametric excitation of mechanical oscillations.

## Contribution

It proposes a new zero-phase-difference Josephson junction utilizing a movable superconducting dot and demonstrates supercurrent flow driven by spontaneous symmetry breaking.

## Key findings

- Supercurrent can flow at zero phase difference due to symmetry breaking.
- Mechanical oscillations synchronize with charge oscillations, enabling coherent Cooper pair transfer.
- Supercurrent direction can be reversed without parameter changes.

## Abstract

Recent advances have attracted attention to non-standard Josephson junctions in which a supercurrent can flow despite zero phase difference between the constituent superconducting leads. Here, we propose a zero-phase-difference nanoelectromechanical junction which, in contrast to other considered systems, exhibits symmetry between leftward and rightward tunneling through the junction. We show that a supercurrent is nevertheless possible as a result of spontaneous symmetry breaking. In the suggested junction, the supercurrent is mediated by tunneling via a superconducting Cooper-pair box on a bendable cantilever. An alternating electric potential parametrically excites mechanical oscillations which are synchronized with charge oscillations of the box. This leads to coherent transfer of Cooper pairs through the junction. The direction of the supercurrent is a result of spontaneous symmetry breaking and thus it can be reversed without changing the parameters.