Imaging of order parameter induced $\pi$ phase shifts in cuprate superconductors by low-temperature scanning electron microscopy

TL;DR

This paper demonstrates that low-temperature scanning electron microscopy can image the supercurrent distribution in cuprate Josephson junctions, revealing the sign change of the order parameter through $$ and $\u2212\u0010$ phase shifts.

Contribution

It introduces LTSEM as a tool to visualize the sign change of the superconducting order parameter in cuprate Josephson junctions, providing direct imaging of $$ and $\u2212\u0010$ phase shifts.

Findings

LTSEM images show Josephson current counterflow in 0 and $$ facets.

Zero magnetic field suppresses critical current in zigzag devices.

Imaging technique can be applied to other Josephson junctions.

Abstract

Low-temperature scanning electron microscopy (LTSEM) has been used to image the supercurrent distribution in ramp-type Josephson junctions between Nb and either the electron-doped cuprate Nd$_{2-x}$Ce$_x$CuO$_{4-y}$ or the hole-doped cuprate YBa$_2$Cu$_3$O$_7$. For zigzag-shaped devices in the short junction limit the critical current is strongly suppressed at zero applied magnetic field. The LTSEM images show, that this is due to the Josephson current counterflow in neighboring 0 and $\pi$ facets, which is induced by the $d_{x^2-y^2}$ order parameter in the cuprates. Thus, LTSEM provides imaging of the sign change of the superconducting order parameter, which can also be applied to other types of Josephson junctions.