A cryogenic microwave scanning near-field probe: Application to study of high-T-c superconductors

We report a vacuum cryogenic (80 K < T < 350 K), near-field microwave scann ing system based on a 90 GHz transmitting/receiving resonant slit antenna w ith a capacitive measurement of the probe-sample separation. The probe allo ws local measurement of resistance as a function of temperature with the sp atial resolution of 20-50 mu m. The mm-wave probe is integrated with the ed dy-current probe which allows global measurement of resistance of conductin g and superconducting samples. This integrated probe is used for local stud y of the superconducting transition in high-T-c superconducting thin films. The sensitivity of our present mm-wave probe is sufficient for probing con ductivity in the normal state and in the superconducting state close to T-c however not yet sufficient for probing conductivity variations far below s uperconducting transition temperature. (C) 1999 American Institute of Physi cs. [S0034-6748(99)00611-5].