Valley-polarized and angle-tunable crossed Andreev reflection in 8-Pmmn borophene

We theoretically investigate the crossed Andreev reflection (CAR) in normal-superconductor-normal (NSN) heterojunctions based on 8-Pmmn borophene with two doping configurations, i.e., nSn and nSp, and modulate the CAR effect exclusively through the pure geometric means of tuning the junction orientation angle without relying on external fields. Two quantum transport phenomena distinct from conventional graphene-based systems are observed due to the anisotropic band structure, i.e., interband retro-CAR and intraband specular-CAR, and the CAR types can be modulated by the junction orientation angle. Moreover, perfect CAR is achieved across a wide range of incident angles. Notably, the CAR response exhibits strong valley-polarized behavior, with significant differences observed between the k_D and -k_D valleys.