Frequency and temperature dependence of the millimeter wave conductivity of epitaxial YBa2Cu3O7 films

TLDR: A millimeter wave spectrometer for frequencies between 100 and 350 GHz consisting of continuously tunable backward wave oscillators as sources and a quasi-optical interferometer in the Mach-Zehnder configuration was used to measure the transmittivity in phase and amplitude of YBa{sub 2}Cu{sub 3}O{sub 7} thin films on NdGaO(sub 3) substrates as mentioned in this paper.

Abstract: A millimeter wave spectrometer for frequencies between 100 and 350 GHz consisting of continuously tunable backward wave oscillators as sources and a quasioptical interferometer in the Mach-Zehnder configuration was used to measure the transmittivity in phase and amplitude of YBa{sub 2}Cu{sub 3}O{sub 7} thin films on NdGaO{sub 3} substrates. From the measured spectra the authors derived the real and imaginary part of the dynamic conductivity {sigma} = {sigma}{sub 1} + {sigma}{sub 2} in the superconducting state as a function of temperature. The {sigma}{sub 1}(T) and {sigma}{sub 2}(T) values at 300 GHz were compared to corresponding values at 19 GHz determined by surface impedance measurements of the same films using a shielded dielectric resonator. The observed frequency dependence of both {sigma}{sub 1}(T) and {sigma}{sub 2}(T) is consistent with a strong reduction of the quasiparticle scattering rate {tau}{sup {minus}1}(T) with decreasing temperature below {Tc}.