Raman and infrared results on YBa₂Cu₃O_7-x type materials

Abstract

We report both Raman and infrared results on the same semiconducting YBa2Cu3O7-x material. With the appropriate heat treatment, this material can be reversibly changed from an orthorhombic superconductor (x≈0.0) to a semiconductor (x>0.5). In the semiconducting material it is easier to measure the phonon features using either technique, and we observe almost the number of modes allowed. By simultaneously considering the modes observed by both techniques, using group theory to sort out the modes in both phases, and using projection operators to determine the symmetry adapted vectors, we arrive at an understanding of some of the modes. We find few differences when comparing our results to other measurements in the superconducting phase. The two general conclusions that we arrive at are: 1) splittings of the modes due to lowering the symmetry from tetragonal to the superconducting orthorhombic phase are not observed; 2) no frequency renormalizations, of the type that have been discussed theoretically, are observed. © 1987.