Microwave heating-induced DC magnetic flux penetration in YBa${}_2$Cu${}_3$O${}_{7-\delta }$ superconducting thin films

Abstract

The magneto-optical imaging technique is used to visualize the penetration of the magnetic induction in YBa${}_2$Cu${}_3$O${}_{7-\delta }$ thin films during surface resistance measurements. The in-situ surface resistance measurements were performed at 7 GHz using the dielectric resonator method. When only the microwave magnetic field $H_{rf}$ is applied to the superconductor, no $H_{rf}$-induced vortex penetration is observed, even at high rf power. In contrast, in the presence of a constant magnetic field superimposed on $H_{rf}$ we observe a progression of the flux front as $H_{rf}$ is increased. A local thermometry method based on the measurement of the resonant frequency of the dielectric resonator placed on the YBa${}_2$Cu${}_3$O${}_{7-\delta }$ thin film shows that the $H_{rf}$--induced flux penetration is due to the increase of the film temperature.

6 pages, Journal of Applied Physics