Non-Centrosymmetric Superconductors

Abstract

Tunneling spectroscopy at surfaces of unconventional supe rconductors has proven an invaluable tool for obtaining information abo ut the pairing symmetry. It is known that mid gap Andreev bound states manifest itself as a zero bias conductance peak in tunneling spectroscopy. The zero bias conduct ance peak is a signature for a non-trivial pair potential that exhibits different si gns on different regions of the Fermi surface. Here, we review recent theoretical resul ts on the spectrum of Andreev bound states near interfaces and surfaces in non-ce ntrosymmetric superconductors. We introduce a theoretical scheme to calculate the nergy spectrum of a non-centrosymmetric superconductor. Then, we discuss th e interplay between the spin orbit vector field on the Fermi surface and the order para meter symmetry. The Andreev states carry a spin supercurrent and represent a hel ic l edge mode along the interface. We study the topological nature of the resulting ed e currents. If the triplet component of the order parameter dominates, then the helica l dge mode exists. If, on the other hand, the singlet component dominates, the heli cal dge mode is absent. A quantum phase transition occurs for equal spin singlet and triplet order parameter components. We discuss the tunneling conductance and the An dreev point contact conductance between a normal metal and a non-centrosymmetr ic superconductor. Matthias Eschrig (a) Fachbereich Physik, Universität Konstanz, D-78464 Ko nstanz, Germany, and (b) Institut für Theoretische Festkörperphysik and DFGCenter for Functional Nanostructures, Karlsruhe Institute of Technology D-76128 Karlsruhe, Germ any, e-mail:Matthias.Eschrig@kit.de Christian Iniotakis Institute for Theoretical Physics, ETH Zurich, 8093 Zurich , Switzerland, e-mail:iniotaki@phys.ethz.ch Yukio Tanaka Department of Applied Physics, Nagoya University, Nagoya, 464-8603, Japan e-mail:ytanaka@nuap.nagoya-u.ac.jp