Electronic structure and phonon behaviour under pressure in YBa 2Cu 4O 8

Abstract

The electronic structure of the high- T c superconductor YBa 2Cu 4O 8 and its change under pressure have been determined within the local density approximation (LDA) to density functional (DF) theory using the full-potential Linearized Muffin Tin Orbital (LMTO) method. The pressure dependence of the energy positions of the plane-derived and chain-derived bands which lie close to and cross the Fermi energy indicates the existence of a hole transfer from the CuO chains and ionic elements to the CuO 2 planes with a rate that diminishes as pressure increases. The behaviour of the frequencies of the Cu(2) and apical-oxygen modes under pressure which have recently been described in Raman measurements are studied in the framework of the Frozen Phonon Approximation. The agreement with experiment shows that the intricate mechanisms involved as pressure varies (charge transfer and changes to the lattice dynamical properties) can be well described by state of the art electronic structure calculations which treat the many-body Coulomb interactions within the LDA.