Absence of diode effect in chiral type-I superconductor NbGe2

TL;DR

This study investigates the absence of the superconducting diode effect in NbGe2, revealing that vortex dynamics significantly influence nonreciprocal transport, with diode efficiency only emerging at high magnetic fields.

Contribution

It demonstrates that vortex dynamics are crucial for the superconducting diode effect, challenging the notion that symmetry breaking alone suffices.

Findings

Negligible diode efficiency at low magnetic fields.

Significant diode efficiency (~50%) at high magnetic fields.

Vortex creep rate increases when bulk superconductivity is suppressed.

Abstract

Symmetry elegantly governs the fundamental properties and derived functionalities of condensed matter. For instance, realizing the superconducting diode effect (SDE) demands breaking space-inversion and time-reversal symmetries simultaneously. Although the SDE is widely observed in various platforms, its underlying mechanism remains debated, particularly regarding the role of vortices. Here, we systematically investigate the nonreciprocal transport in the chiral type-I superconductor NbGe2. Moreover, we induce type-II superconductivity with elevated superconducting critical temperature on the artificial surface by focused ion beam irradiation, enabling control over vortex dynamics in NbGe2 devices. Strikingly, we observe negligible diode efficiency (Q < 2%) at low magnetic fields, which rises significantly to Q ~ 50% at high magnetic fields, coinciding with an abrupt increase in vortex creep rate when the superconductivity of NbGe2 bulk is suppressed. These results unambiguously highlight the critical role of vortex dynamics in the SDE, in addition to the established symmetry rules.