Photothermal measurements of differential reflectivity of YBCO related to the symmetry of the superconducting order parameter

Abstract

We have investigated symmetry of the differential optical response of single YBCO domains in the a-b plane. As a function of temperature, this response consists of a smooth background and a sharp peak in the vicinity of Tc related to the normal and superconducting phases, respectively. For the probe light polarized along the a axis, we have observed for the first time that the superconducting phase response is a sharp peak near Tc which is only ∼ 1 K wide. It is difficult to explain this peak in terms of a single second-order phase transition, or to arrive at a suitable model to explain the experimental results. We have also measured cross-polarized DOR signals which showed no off-diagonal reflection components.