Spatially resolved differential resistance of bulk superconductors by laser-induced heating

Spatially resolved measurements of the change in resistance with temperature of bulk high-temperature superconductors are generated by heating a localized region of a sample with a modulated laser beam. The amplitude of the thermally induced resistance change is related to the heat capacity and derivative of resistance with temperature whereas the phase of the signal is related to the thermal diffusivity of the sample. By moving the sample with respect to the focused laser beam, spatially resolved measurements may be made. Images with ∼50-μm resolution have been used to locate defects in polycrystalline Bi-Sr-Ca-Cu-O sample and to estimate the thermal diffusivity of the bulk material