Infrared and Raman spectra of the MBa 2Cu 3O 7-type high-T c superconductors

Abstract

Infrared and Raman spectra of superconducting MBa 2Cu 3O 7 (M = Y, Sm, Eu, Gd, Ho) have been measured at several temperatures between 4 and 300 K. Contrary to the Raman spectra, the ir spectra display upon cooling below 80 K structure which seems characteristic of the superconducting gap starting at ∼210 cm -1 and below. A number of phonons are observed in both spectra, mostly as Davydov pairs. They are attributed to stretching and bending vibrations of Cu-O bonds and vibrations of the Ba and M atoms along the x, y, and z directions. The Cu-O bonds also yield one set of ir-active stretching and bending modes without Davydov conjugate. The vibrations of the M atom along x, y, z yield only ir-active modes. These results are compared with those for the non-superconducting tetragonal YBa 2Cu 3O 6 compound.