The Use of Low Temperature Scanning Microscope for Estimating In-Plane Thermal Diffusivity in YBCO Thin Film

We have experimentally investigated thermal diffusion in a SrTiO₃ based YBCO bicrystalline thin-film by means of one-dimensional low temperature scanning microscope (LTLSM). Grain boundary (GB) being a weak link is temperature sensitive, thus it can be used as a local thermal sensor. In experiments DC bias current was higher than the GB critical current, but much lower than the intra-grain one. At 10 Hz modulation frequency the detected GB trace was found to be about 300 micrometers. Upon the frequency increase, the trace diminishes and for 200 kHz was about 10 micrometers. Theoretical analysis shows that thermal length varies inversely as the square root of the frequency, and phase delay is in direct proportion. We have shown phase delay between modulating and response signals to be in a good agreement with theoretical frequency dependence. Effective thermal diffusivity coefficient calculated from the above dependence is close to that of the SrTiO₃ and indicates that heat diffusion is much influenced by the substrate. Hence this result demonstrates the potential of the LTLSM for obtaining effective in-plane thermal diffusivity of multilayered superconducting tapes and films.