Andreev reflection in topological nodal-line semimetals superconductor junction

Abstract

Abstract Andreev reflection is an important quantum tunneling phenomenon in the conductor-superconductor junction. The Andreev reflection coefficients TAR of a hybrid system with s-wave superconductor connected by topological nodal-line semimetals (TNLSMs-SC junction system) is calculated theoretically by using the Landauer-Büttiker formula combined with the nonequilibrium Green’s function method. The results show that when the direction of the boundary state electron and the incident electron are the same, only the bulk states of the TNLSMs involve the Andreev reflection of the hybrid system, and the Andreev reflection coefficients TAR enhance with the increase of the Fermi energy EF . We also study the effect of on-site energy µz and mass term m on the Andreev reflection and find that the Andreev reflection in the system decreases rapidly with the increase of on-site energy µz and mass term m. Moreover, we find that only in the presence of a mass term m, the Andreev reflection coefficients TAR of the system changes with the rise of the Fermi energy EF . When a perpendicular magnetic field is applied in the system, the Andreev reflection coefficients TARin the superconducting gap will appear a series of oscillating peaks. For a hybrid system with the large perpendicular magnetic field applied, we find that the maximum Andreev reflection coefficients TAR=7.2 at the Fermi energy EF = 0.0 and the incident electron energy E = ±0.1. The Andreev reflection coefficients TAR is gradually enhanced in the superconducting gap (incident energy |E| ≤ 0.2) when a disorder is applied to the superconductor region of the system. However, the symmetry of the Andreev reflection coefficients TARis broken when the perpendicular magnetic field is applied to the system. These peculiar transport properties of the TNLSMs-SC junction system are expected to provide theoretical guidance for future applications.