Calculation of spin states of photoelectrons emitted from spin-polarized surface states of Bi(111) surfaces with a mirror symmetry

Spin states of photoelectrons excited from spin-polarized surface states of Bi(111) surfaces are theoretically studied. The electronic states with a mirror symmetry are focused on in particular. We present a method for calculating spin expectation values of photoelectrons using results of density-functional methods in the plane-wave basis. We show that the free-electron approximation for final states is not sufficient for explaining an experimental result obtained in spin- and angle-resolved photoelectron spectroscopy. We point out two effects of the time-reversal symmetry in photoelectron emission. One is that the out-of-plane component of spin orientation is reversed to that of the time-reversed state. This property may be used for distinguishing the orientation of samples by shedding light with polarizations that break the mirror symmetry. Another is the asymmetry in photoemission intensity between an initial state and its time-reversed state due to the breaking of the time-reversal symmetry intrinsic in the photoemission process.