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 M

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 YBa₂Cu₃O_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 YBa₂Cu₃O_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.