We have unambiguously observed the c -axis Josephson plasma resonance (JPR) in high-critical-temperature (<i>T</i><sub>c</sub>) cuprate (Tl<sub>2</sub>Ba<sub>2</sub>CaCu<sub>2</sub>O<sub>8</sub>) 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-<i>T</i><sub>c</sub> material in transmission. With increasing temperature, the JPR shifts from 705 GHz at 10 K to ~170 GHz at 98 K, corresponding to an increase in c-axis penetration depth from 22.4±0.6μm to 94±9μm . 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 ~0.95T<sub>c</sub> . The JPR vanishes above T<sub>c</sub> as expected.
© 2001 Optical Society of America
V. K. Thorsmølle, R. D. Averitt, M. P. Maley, L. N. Bulaevskii, C. Helm, and A. J. Taylor, "C-axis Josephson plasma resonance observed in Tl2Ba2CaCu2O8 superconducting thin films by use of terahertz time-domain spectroscopy," Opt. Lett. 26, 1292-1294 (2001)