Infrared phonon structure in epitaxial films of Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub 10} at low temperatures

Abstract

We have used both bolometric and cavity techniques to obtain accurate submillimeter and microwave loss data for epitaxial thin films of Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub 10} at low temperatures. These films have {Tc}=121.5 K, are c-axis oriented, contain some volume fraction of the 2:1:2:2 phase, and are characterized by excellent in-plane epitaxy. The absorptivity of these films at 100 cm{sup {minus}1} is a factor of five lower than that obtained by others from a reflectivity measurement on a ceramic sample. We observe strong phonon structure for frequencies between 70 and 600 cm{sup {minus}1}, which are in agreement with a lattice dynamical calculation. Our results show remarkably similar phonon structure to that observed in the ceramic sample. This is in strong contrast to the case for other high {Tc} superconductors such as YBa{sub 2}Cu{sub 3}O{sub 7}, where phonon structure observed in ceramic samples in absent in epitaxial oriented films and crystals because of the electronic screening due to the high conductivity of the a-b planes. At microwave frequencies the absorptivity follows a frequency squared dependence, and is consistent with the submillimeter results. 6 refs.