Huge Rashba-type spin-orbit coupling in binary hexagonal PX nanosheets (X = As, Sb, and Bi).

We theoretically propose that Rashba-type band splitting can be achieved in binary alloyed hexagonal PX nanosheets (X = As, Sb, and Bi). The lack of inversion symmetry results in an effective electric field perpendicular to the basal plane of PX, hence, leading to Rashba-type spin-orbit coupling (SOC) in the two dimensional PX nanosheets. Since the SOC strength roughly scales quadratically with atomic number, the largest band splitting is found in PBi with a Rashba coefficient of ∼1.56 eV Å, which is a huge value among two-dimensional materials. Furthermore, tensile biaxial strain can be employed to significantly enhance the strength of SOC, for instance, a Rashba coefficient of 4.41 eV Å can be realized at a strain of 10%. The huge and strain-tunable Rashba-type SOC of PBi suggests that it holds great promise for spintronic applications.