Orthorhombic Distortion at the Superconducting Transition in YBa2Cu3O7: Evidence for Anisotropic Pairing

Abstract

We report the results of a high-resolution x-ray scattering study of the structure of Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ as a function of temperature. We find that there is an anomaly in the orthorhombic splitting, $b-a$, near the superconducting transition, whereas there is little or no anomaly in the unit-cell volume. Our results suggest that the superconducting wave function has a uniaxial anisotropy within the $a-b$ plane.