Effect of LaAlO$_3$ Surface Topography on RF Current Distribution in Superconducting Microwave Devices

TL;DR

This study investigates how the surface topography of LaAlO$_3$ substrates affects rf current distribution in superconducting microwave devices, revealing that substrate twinning causes current meandering and local rf response enhancement.

Contribution

It provides detailed analysis of substrate twinning effects on current distribution and nonlinear response in superconducting microwave resonators, using laser scanning microscopy.

Findings

Twinning causes meandering of rf current at edges.

Substrate irregularities lead to ~20% rf photoresponse enhancement.

Edge irregularities may contribute to device nonlinearities.

Abstract

A laser scanning microscope with a thermal spot size of about 4 $\mu$m is used to measure a quantity proportional to the rf current density in an operating superconducting co-planar waveguide microwave resonator. The twinning of the LaAlO$_3$ substrate produces a meandering of the current at the edges due to irregularities in the wet etching of the YBa$_2$Cu$_3$O$_{7-\delta}$ film associated with substrate twin domain blocks, and a ($\sim$ 20%) enhancement of the rf photoresponse at these locations. These irregularities are candidates for enhanced nonlinear response from the device. The effects of substrate twinning and the resulting edge features on the superconducting film are discussed and analyzed.