Seminars & Colloquia

Detection and Control of Broken Symmetries with Andreev Bound State Planar Tunneling Spectroscopy

Laura H. Greene
Department of Physics and Materials Research Laboratory
University of Illinois at Urbana-Champaign
Urbana, IL 61801 USA
Monday 21 April 4:00 pm Higgins 310

Quasiparticle planar tunneling spectroscopy is shown to be a powerful, phase-sensitive spectroscopic tool for the study of unconventional superconductivity. Several familiar and novel junction fabrication techniques on YBCO thin films and BSCCO single crystals are used for our systematic studies of the tunneling conductances, which are obtained as a function of crystallographic orientation, applied magnetic field (magnitude and orientation) atomic substitution, ion-induced damage and physically-induced surface damage. All these results confirm that the observed zero-bias conductance peak (ZBCP) is comprised of Andreev bound states (ABS), which arise from reflection-symmetry breaking at a d-wave superconductor interface.

Consistency in the observation of the spontaneous and field-induced splitting of the ZBCP is presented. We show, based on our own data and from a survey of the literature, that these splittings occur concomitantly in a given junction. We show how the observation of the splitting can be controlled with the length-scale of the surface disorder and the magnitude of the tunneling cone. The Doppler effect accounts for the field induced splitting and the spontaneous splitting data are consistent with models of spontaneous broken time-reversal symmetry.