Quantum Interference of Rashba-Type Spin-Split Surface State Electrons

We studied the quantum interference of electrons in the Bi (pₓ,py) orbital-derived $j=1/2$ spin-split surface states at Bi/Ag(111)√3×√3 surfaces of 10 monolayer thick Ag(111) films on Si(111) substrates. Surface electron standing waves were observed clearly at the energy (E) below the intersection of the two spin-split downward dispersing parabola bands (Eₓ). The E dependence of the standing wave pattern reveals the dispersion as the average of the two spin-split surface bands due to the interference between |(k+Δ),↑⟩ and |-(k-Δ),↑⟩ [or (|(k-Δ),↓⟩) and |-(k+Δ),↓⟩] states. In contrast, it was impossible to deduce the dispersion from the standing wave pattern at E≥Eₓ because the surface electron cannot find its backscattered state with the same spin polarization.