Spontaneous voltage peaks in superconducting Nb channels without engineered asymmetry

TL;DR

This study reports spontaneous voltage peaks in plain Nb superconducting channels at the transition, caused by an unconventional nonreciprocal transport mechanism that does not require engineered asymmetry or magnetic fields.

Contribution

It reveals a novel spontaneous nonreciprocal effect in superconducting Nb channels, challenging the typical requirement of structural asymmetry or magnetic fields.

Findings

Spontaneous voltage peaks observed at superconducting transition.

Voltage peaks are symmetric in magnetic field, even at zero field.

Indicates an unconventional nonreciprocal transport mechanism.

Abstract

Rectification effects in solid-state devices are a consequence of nonreciprocal transport properties. This phenomenon is usually observed in systems with broken inversion symmetry. In most instances, nonreciprocal transport arises in the presence of an applied magnetic field and the rectified signal has an antisymmetric dependence on the field. We have observed rectification of environmental electromagnetic fluctuations in plain Nb channels without any asymmetry in design, leading to spontaneous voltage peaks at the superconducting transition. The signal is symmetric in the magnetic field and appears even without an applied field at the critical temperature. This is indicative of an unconventional mechanism of nonreciprocal transport resulting from a spontaneous breaking of inversion symmetry.