Investigation of Dynamic Behaviors of Low-Level Dissipation at ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7}$ Grain Boundaries Using Low-Temperature Near-Field Scanning Microwave Microscopy

Near-field scanning microwave microscopy (NSMM) provides a unique nondestructive approach for detection of local dissipation with high sensitivity and high spatial resolution. With recently improved NSMM probes of spatial resolution of up to 400 nm ( ~ 10 -6 wavelength), detection of dissipation was achieved on YBCO microbridges at currents more than three orders of magnitude below the Jc ( T ). In this work, we report characterization of the dynamic behavior of low-level dissipation at the grain boundary of YBa 2 Cu 3 O 7-δ microbridges as function of time and applied electrical current. On higher-angle grain boundary, the dissipation develops rapidly with increasing current and shows approximately linear dependence on current. On lower-angle grain boundary, nonlinear features were observed and attributed to bi-modal pattern of dissipation evolution of nucleation of isolated hot spots and their evolution. Comparison with the similar NSMM+ IV measurement made on the “bulk” part of the same YBa 2 Cu 3 O 7-δ microbridges on a reduced temperature scale shows higher dissipation on the grain boundary can be mostly attributed to the lower Tc values on grain boundaries.