Transverse voltage and chiral glass transition in YBa2Cu3O6+d thin films

We report on measurements of the voltage difference between non-aligned electrical contacts placed on opposite edges of several YBa2Cu3O6+d (YBCO) thin films prepared by a chemical method. The experiments were performed while the samples were traversed by a longitudinal electrical current. Experiments are focused on the region of the superconducting transition. In many cases these transverse voltage results do not reproduce the measurements carried out with the conventional geometry, where the voltage contacts are aligned along the current orientation. An excess transverse voltage was identified in a narrow temperature range encompassing the critical temperature. The sign and detailed shape of the excess transverse voltage vary from sample to sample. The application of a magnetic field perpendicular to the film surface suppresses the effect above a certain field threshold. The shape and magnitude of the excess transverse voltage peaks are also strongly modified or suppressed in samples submitted to implantation with oxygen ions or to a slight deoxygenation process. The simplest models considering the occurrence of a transverse current flow generated by film inhomogeneities cannot explain the totality of the obtained results. We thus suggest an interpretation of the excess transverse voltage effect based on the stabilization of a chiral-glass superconducting phase in the studied YBCO films. The occurrence of this state is related to the submicron granularity that characterizes the microstructure of these films.