CPM Seminar

Nanoscale Probe of Chiral d-wave Pairing in a Cuprate Superconductor

John Wei

University of Toronto & Canadian Institute for Advanced Research

Cooper pairs in superconductors are generally composed of time-reversed electrons. This time-reversal invariance can be violated when the pairing symmetry is complex, corresponding to the appearance of a spontaneous orbital current. Recent interest has been on the chiral symmetry of complex p-wave and d-wave pairing, which are believed to occur in ruthenate and cuprate superconductors, since chiral states could be useful for topological quantum computing. In this talk I will present a nanoscale measurement, using cryomagnetic scanning tunnelling spectroscopy, of the topological surface states due to d-wave Andreev reflection on thin films of superconducting Ca-doped YBa₂Cu₃O₇. We observed various spectral behaviors with distinct magnetic field evolutions, indicating that the orbital current which violates time-reversal invariance is inhomogeneous and perturbable at coherence length scales. Remarkably, this local orbital current appears to flow in only one of the two allowed chiralities, suggesting that it may be possible to form and manipulate nanoscale domains of chiral d-wave pairing by either field or current.