Graphite-superconductor junctions as a probe of order-parameter symmetry

Abstract

We discuss a method for determining the order-parameter symmetry of quasi-one-and quasi-twodimensional unconventional superconductors by the use of graphite-superconductor junctions. The use of a graphite gate voltage, in combination with a bias tunneling voltage, allows access to more information concerning gap values on the Fermi surface than with conventional tunneling spectroscopy, where only a bias voltage is employed. In particular, the use of a gate voltage allows one to tune the momentum-space size of the tunneling region, thus accessing gap values over local regions of the superconductor Fermi surface, in contrast to conventional tunneling techniques.

Proposed experiment: out-of-plane nodal lines in Sr$_{2}$RuO$_{4}$

“…The method is based on tunneling spectroscopy, which can be a strong probe of order parameter symmetry. The basis of the experiment is presented in Figure 1 (reprinted from 11 ), which depicts, in momentum space, an Sr 2 RuO 4 c-axis tunneling spectroscopy ex-periment, based upon a recent proposal 11 by the author and P. Thalmeier for the use of graphite as a normal electrode in a superconducting-insulator-graphite tunneling experiment. As the method is described in detail in that publication I only sketch the proposal here.The basic idea is that the use of a gate voltage applied to the semi-metal graphite changes the length of the electron-occupied graphite HKH Fermi surface "cigar".…”