Influence of Columnar Defects on Magnetic Relaxation of Microwave Nonlinearity in Superconducting YBCO Resonator Devices

TL;DR

This study investigates how columnar defects in YBCO superconducting resonators affect magnetic flux relaxation and microwave nonlinearity, revealing defect-induced flux pinning and suppression of IMD relaxation.

Contribution

It demonstrates that columnar defects suppress fluxon relaxation and alter microwave intermodulation distortion behavior in superconducting YBCO devices.

Findings

Columnar defects pin fluxons, reducing relaxation.

Relaxation of IMD varies with defect presence and temperature.

Third order IMD relaxation is suppressed at low temperatures with defects.

Abstract

Intermodulation distortion (IMD) of microwave signals incident upon a superconducting YBa2Cu3O7 thin film sample on a LaAlO3 substrate is shown to relax as the sample magnetization also relaxes, revealing the signature of fluxon decay in the microwave distortion. The sample contained a microchannel of columnar defects that was introduced using heavy ion beam irradiation. After exposure to and then removal of a low strength static magnetic field, IMD relaxed due to thermal activation of fluxons over the surface barrier. This process influenced second and third order IMD differently, visible in the differing functional form of the IMD in time and the temperature dependence of the relaxation function. The presence of columnar defects in the test sample suppressed thermal activation by pinning of fluxons, notably with complete suppression of relaxation in third order IMD at low temperatures. Higher order IMD was found to relax with the same functional form as the second and third order IMD of the same parity.