Tunneling conductance in graphene based FNS junction with time-reversal symmetry broken

Abstract

Motivated by recent experimental advances in graphene superconducting junctions with time-reversal symmetry broken (TRSB), we investigate the tunneling conductance in graphene-based ferromagnet-normal metal-superconductor junction with TRSB. It is found that in the absence of Fermi wave mismatch (FWM), the tunneling conductance is suppressed by exchange field of ferromagnet for all pairing states including one time-reversal symmetry D-wave state and two time-reversal symmetry broken, i.e. D+iS and D+iDxy states. Also, in the presence of FWM, the increase of the exchange field leads to an enhancement in tunneling spectra. Moreover, we have found that the subdominant orders play a crucial role such that by adjusting bias voltages at energies in the Dirac-points, tunneling conductance can help discriminate D+iS from D+iDxy. In addition, we have obtained that the width of normal metal (intermediate layer) makes a noticeable change in tunneling spectra especially when the angle of superconducting crystal with respect to x-axis, is placed in (110)-direction. Also, the increase of intermediate layer thickness causes the oscillations to appear in tunneling spectra. Therefore, by tuning the junction parameters and the applied bias voltage, not only is it possible to understand more about the pair potentials with TRSB, but the obtained tunneling spectra may serve as a tool to differentiate between TRSB states and non-TRSB ones.