Frequencies, eigenvectors, and single-crystal selection rules of k=0 phonons in YBa2Cu3O7−δ: Theory and experiment

Abstract

We have determined the components of the Raman tensor of signal-crystal superconducting ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ for the phonons at ∼500, 440, 330, and 150 ${\mathrm{cm}}^{\mathrm{-}1}$. They all correspond to the totally symmetric modes both in the tetragonal ($A_{1g}$) and orthorhombic ($A_g$) structures except for the 330-${\mathrm{cm}}^{\mathrm{-}1}$ mode which is $B_{1g}$ tetragonal. We have also performed lattice dynamical calculations with parameters extracted from those of perovskite and other metallic oxides. The frequencies and eigenvectors obtained agree well with the experimental results. This work settles discrepancies found in the previous literature.