Andreev reflections in black phosphorus based normal-superconducting junctions modulated by linearly polarized light

We perform investigations about the Andreev reflections (ARs) in normal-superconducting (NS) junctions based on the few-layer black phosphorus, by considering the irradiation of the linearly polarized off-resonant light. Following the analysis on the band structures, we propose the types of ARs in such NS junctions. Specifically, it has been found that when the incident energy E is less than the Fermi energy EF, the intraband retro AR occurs, and otherwise the interband specular AR is achieved. A forbidden region of ARs is formed between the retro AR and the specular AR since the band gap leads to a momentum-filtering feature. By using the linearly polarized off-resonant light along y direction, we are allowed to modify the size of this forbidden region. On the other hand, when the normal direction of the NS-junction interface is changed from parallel to perpendicular, by using the linearly polarized off-resonant light along x direction, the retro and specular ARs can be transformed into each other, resulting in an anisotropic differential conductance, which is a unique observable signature for AR in the experiment.