RAMAN-ACTIVE PHONONS OF A TWIN-FREE YBA2CU3O7 CRYSTAL - A COMPLETE POLARIZATION ANALYSIS

A complete Raman analysis has been performed on a high-quality YBa2Cu3O7 crystal made free of twins by a mechanical detwinning process. Marked a-b anisotropy is observed in the intensity of the Ag phonons at 116, 335, and 495 cm-1. At room temperature, the ±yy component of the polarizability tensor of the 116-cm-1 phonon is strongly coupled to an electronic continuum, the ±xx component is less strongly coupled, and the coupling of the ±zz component is not apparent in the Raman line shape. B2g and B3g phonon pairs are reproducibly found at 70 and 83 cm-1, 142 and 140 cm-1,210 and 303 cm-1, and 579 and 526 cm-1. Comparison of the observed B2g-B3g pairs to literature calculations of frequencies is made. © 1990 The American Physical Society.