  Micro-channels of nanosized columnar tracks were planted by heavy-ion
irradiation into superconducting microwave microstrip resonators that were
patterned from YBa2Cu3O7-x thin films on LaAlO3 substrates. Three different ion
fluences were used, producing different column densities, with each fluence
having a successively greater impact on the nonlinearity of the device, as
compared to a control sample. Photoresponse images made with a 638 nm rastered
laser beam revealed that the channel is a location of enhanced photoresponse
and a hot spot for the generation of intermodulation distortion. The microwave
photoresponse technique was also advanced in this work by investigating the
role of coupling strength on the distribution of photoresponse between
inductive and resistive components.
