Lattice dynamics of high-Tc superconductors: Optical modes of the thallium-based compounds

Abstract

We present a lattice-dynamical calculation of the Raman- and infrared-active modes of the following six thallium-based high-Tc superconductors: Tl2Ba2CuO6, Tl2CaBa2Cu2O8, and Tl2Ca2Ba2Cu3O10 (body-centered-tetragonal structures) and TlCaBa2Cu2O7, TlCa2Ba2Cu3O9, and TlCa3Ba2Cu4O11 (simple-tetragonal structures). Our calculations are based on a shell model that incorporates short-range overlap potentials, long-range Coulomb potentials, and ionic polarizabilities. We also require that the shell models for different high-Tc superconducting compounds be mutually compatible, namely that the short-range potentials for given ion pairs in equivalent environments be transferable from one compound to the other. The model presented here does in fact utilize a common set of short-range potentials that apply to the entire series of thallium-based superconductors as well as to YBa2Cu3O7 and Bi2CaSr2Cu2O8, studied earlier. The model reproduces the available experimental infrared and Raman data of all these compounds quite well and is thus supported by a broad database, albeit only of optical modes. We expect that our model, which is based on realistic interaction potentials, reproduces eigenvalues and eigenvectors to the same approximation. Thus we conclude from the satisfactory agreement between calculated and measured eigenfrequencies that the calculated eigenvectors provide a realistic description of the displacement patterns of the optical modes.

Source-reported materials — not catalogue approval

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