Raman study of the phonon anomaly in single-crystalYBa2Cu3O7−δin the presence of a magnetic field

Abstract

The frequency of the 340-${\mathrm{cm}}^{-1\mathrm{}}$ Raman-active O(II)-O(III) ($z$) out-of-phase mode in single-crystal $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ is measured as a function of magnetic field ($B\leqq 12.7 \mathrm{T}$) and temperature. We reproduce the well-established softening of this mode at $T_c$ and confirm that this anomaly is connected with superconductivity since it reflects the usual $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ relation. This provides additional evidence for the copper-oxygen planes being the crucial elements for superconductivity in this material. It also suggests strong coupling of this Raman phonon with electronic excitations in the superconductor.