Josephson-like behavior in YBa$_2$Cu$_3$O$_{7-\delta}$ nano-bridges carrying the depairing current

TL;DR

This study demonstrates Josephson-like behavior in YBa$_2$Cu$_3$O$_{7-\delta}$ nano-bridges, revealing critical current properties and Shapiro steps indicative of high-quality superconducting junctions at nanoscale dimensions.

Contribution

It provides experimental evidence of Josephson effects in ultra-narrow YBa$_2$Cu$_3$O$_{7-\delta}$ nano-bridges and compares critical current densities with theoretical models.

Findings

Critical current density matches Ginzburg-Landau depairing current density.

Observation of up to 160 Shapiro-like steps under microwave irradiation.

Critical current increases as bridge width decreases, even below Pearl length.

Abstract

We have investigated the zero-field critical supercurrent of YBa$_2$Cu$_3$O$_{7-\delta}$ bridges patterned from 50 nm thick films as a function of bridge width, ranging from 2 $\mu$m to 50 nm. The critical current density monotonically increases for decreasing bridge width even for widths smaller than the Pearl length. This behavior is accounted for by considering current crowding effects at the junction between the bridge and the wider electrodes. Comparison to numerical calculations of the current distributions in our bridge geometries of various widths yields a (local) critical current density at 4.2 K of $1.3\times 10^8$ A/cm$^2$, the Ginzburg Landau depairing current density. The observation of up to 160 Shapiro-like steps in the current voltage characteristics under microwave irradiation substantiates the pristine character of our nano bridges with cross sections as small as $50\times 50$ nm$^2$.