Infrared phonon structure in epitaxial films of Tl2Ca2Ba2Cu3O10 at low temperatures

摘要

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.