Theory of tunneling conductance of anomalous Rashba metal / superconductor junctions

Abstract

We theoretically study the charge conductance in anomalous Rashba metal (ARM)/superconductor junctions for various types of the pairing symmetries in the superconductor. The exotic state dubbed ARM, where one of the spin resolved Fermi surface is absent, is realized when the chemical potential is tuned both in the presence of Rashba spin-orbit interaction (RSOI) and an exchange field. Although a fully polarized ferromagnet metal (FPFM) is also a system where the electron's spin degrees of a freedom is reduced to be half, the electrons in an ARM have distinct features from those in FPFM. For the ARM/spin-singlet superconductor junctions, the obtained tunneling conductance within the bulk energy gap is enhanced with the increase in the magnitude of the RSOI. In particular, in ARM/$d_{xy}$-wave superconductor junctions, the zero bias conductance peak is enhanced owing to the presence of the RSOI. For ARM/$p_{x}$-wave superconductor junctions, the condition of the existence of the zero bias conductance peak is significantly sensitive to the direction of the d-vector of the $p_{x}$-wave superconductor. Furthermore, the obtained conductance in ARM/chiral $p$-wave superconductor junctions shows different behaviors as compared to those in ARM/helical $p$-wave superconductor junctions. This feature gives a guide to determine the spin structure of the Cooper pair in spin-triplet superconductor Sr$_{2}$RuO$_{4}$.