Spectroscopy of high temperature superconductors at microwave and low far infrared frequencies

The authors study the surface resistance and reactance of high quality YBa2Cu3O7 superconducting films in a transmission line geometry with electrical pulses of ∼ 1-ps duration. The spectrum of these extremely short electrical transients extends from dc to ∼ 1 THz and allows measurement of the complex surface impedance of the superconductor over the same bandwidth. Compared to reflectivity measurements, the transmission line geometry offers the advantage of long interaction length, so that the surface impedance can be measured with high accuracy even for low temperatures. The surface resistance at 77 K determined this way is plotted vs frequency