Supercurrent diode effect in thin film Nb tracks

We demonstrate nonreciprocal critical current in 65 nm thick polycrystalline and epitaxial Nb thin films patterned into tracks. The nonreciprocal behavior gives a supercurrent diode effect, where the current passed in one direction is a supercurrent and the other direction is a normal state (resistive) current. We study the variation of the diode effect with temperature and magnetic field, and find an unexpected dependence with the width of the Nb tracks from 2-10 $\mu$m. For both polycrystalline and epitaxial samples, we find that tracks of width 4 $\mu$m provides the largest supercurrent diode efficiency of up to $\approx30\%$, with the effect reducing or disappearing in the widest tracks of 10 $\mu$m. It is anticipated that the supercurrent diode will become a ubiquitous component of the superconducting computer.