Raman Phonons under Hydrostatic Pressure in YBa₂ (Cu_1-xNi_x) ₄O₈

Abstract

We present a study of the Raman phonons in YBa₂ (Cu_{0. 96}Ni_{0. 04}) ₄O₈ under hydrostatic pressure in the superconducting phase. In contrast to the undoped material, two modes have significantly different pressure coefficients: the O (1) chain mode shifts 35% faster while the O (2) -O (3) in phase mode shifts 33% slower than their undoped counterparts. The other modes shift in a manner similar to the undoped material. We understand this behavior in terms of the smaller compressibility in the vicinity of the chain substituted Cu (Ni) atom.