Giant Rashba-Type Spin Splitting in Bi/Ag(111) from Asymmetric Interatomic-Hopping

Rashba-type spin splitting (RSS) has recently drawn added attention due to its central role in the field of spintronics. In that regards, designing materials with giant RSS is highly desirable for practical spintronic applications, and thus disclosing the origin of the giant RSS could pave the way. Here, we theoretically demonstrate that the giant RSS observed in Bi/Ag(111) alloy system emerges from the difference in kinetic energy or interatomic-hopping strength, not from a uniform electric field. Our density functional theory calculation and tight-binding analysis show that depending on the chirality of orbital angular momentum (OAM), the Bi orbital forms an asymmetric charge distribution in the direction towards or away from the Ag atom. As a result, opposite OAM chirality results in difference in hopping strength between Bi and Ag orbitals, and this kinetic energy difference dominates the size of RSS. This new interpretation on the RSS successfully explains the giant RSS in Bi/Ag(111) surface states and has implication for the RSS mechanism in general.