Non-reciprocal transport and rectification effects in superconducting niobium devices

Asymmetric conductors exhibit non-reciprocal transport, characterized by the fact that the resistance for current flow is different for opposite polarities. A broad range of solid-state systems, including both semiconductors and superconductors, are known to exhibit such properties. In most instances, non-reciprocal transport is seen in the presence of an applied magnetic field, therefore requiring the breaking of both inversion and time reversal symmetries. We have conducted experiments with superconducting niobium films and observed the spontaneous generation of dc voltage resulting from the rectification of environmental fluctuations. This is a signature of non-reciprocal transport, which testifies to the existence of a directional asymmetry within the device. By studying the magnetic-field-dependence of the rectified signal, we determine that the underlying phenomenon involves a spontaneous breaking of inversion symmetry. We will discuss about the possibility of ferroelectricity arising at nanometric lengthscales in niobium films.

Reference : Phys. Rev. B 109, L060503 (2024)