C-axis Josephson plasma resonance observed in Tl2Ba2CaCu2O8 superconducting thin films by use of terahertz time-domain spectroscopy

We have unambiguously observed the c-axis Josephson plasma resonance (JPR) in high-critical-temperature (T-c) cuprate (Tl2Ba2CaCu2O8) superconducting thin films, employing terahertz time-domain spectroscopy in transmission as a function of temperature in zero magnetic field. These are believed to be the first measurements of the JPR temperature dependence of a high-T-c material in transmission. With increasing temperature, the JPR shifts from 705 GHz at 10 K to similar to 170 GHz at 98 K, corresponding to an increase in c-axis penetration depth from 22.4 +/- 0.6 mum to 94 +/- 9 mum. The linewidth of the JPR peak increases with temperature, which indicates an increase in the quasi-particle scattering rate. We have probed the onset of the c-axis phase coherence to similar to0.95 T-c. The JPR vanishes above T-c as expected. (C) 2001 Optical Society of America.