Observation of field-odd and field-free superconducting diode effects in $\mathrm{Mo}_2\mathrm{C}$ nanoflakes

TL;DR

This paper reports the discovery of superconducting diode effects in Mo₂C nanoflakes, including both field-odd and field-free effects, revealing new nonreciprocal supercurrent phenomena in a centrosymmetric material.

Contribution

It demonstrates the existence of intrinsic superconducting diode effects in Mo₂C nanoflakes, a material previously considered centrosymmetric, with potential applications in quantum electronics.

Findings

Field-odd SDE with >40% efficiency at 4 K under magnetic field.

Robust field-free SDE observed at zero field and field-cooling.

Intrinsic nature confirmed by out-of-plane field sweeps.

Abstract

The superconducting diode effect (SDE) enables nonreciprocal supercurrent flow, holding immense potential for ultra-low-power quantum electronics. Intrinsic SDE typically requires materials with inherent symmetry breakings. Here, we report the discovery of SDE in chemical vapor deposition-grown molybdenum carbide ($\mathrm{Mo}_2\mathrm{C}$) nanoflakes, a material traditionally considered centrosymmetric. Strikingly, this system uniquely hosts both field-odd and field-free SDEs. Transport measurements reveal a field-odd SDE with tunable efficiency exceeding 40% at 4 K under a perpendicular in-plane magnetic field. In a separate sample, a robust field-free SDE persists under zero-field and field-coolings. Out-of-plane field sweeps confirm the intrinsic nature of these phenomena. We propose that domain-boundary supercurrents or charge density wave-like orders drive this unexpected combination of symmetry breakings. Our findings establish air-stable $\mathrm{Mo}_2\mathrm{C}$ as an ideal platform for nonreciprocal superconducting electronics operating at liquid-helium temperatures, expanding the search for SDE into nominally centrosymmetric superconductors.