Characterization of local dielectric properties of superconductor YBa2Cu3O7-δ using evanescent microwave microscopy

A near-field evanescent microwave microscope based on a coaxial transmission line resonator with a tungsten tip protruding through an end-wall aperture is used to measure local dielectric properties of thin film YBa₂Cu₃O_7-δ in superconducting state below critical temperature T_c=91 K at T=79.4 K and in normal state at room temperature (T=298 K). The dielectric property of the superconductor within the near field of the tip frustrates the electric field and measurably changes the transmission line´s resonant frequency. The shift of the resonator´s frequency is measured as a function of tip-sample separation and associated change in quality factor (Q) image scans of the thin film is obtained. A quantitative relationship between the real and imaginary parts of the local dielectric constant and the frequency shift using the method of images is established. The comparison between experimental data and theory based on this method is given and discussed for YBa₂Cu₃O_7-δ thin film deposited on LaAlO₃ substrate.