Spin-flip transitions and departure from the Rashba model in the Au(111) surface

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We present a detailed analysis of the spin-flip excitations induced by a periodic time-dependent electric field in the Rashba prototype Au(111) noble metal surface. Our calculations incorporate the full spinor structure of the spin-polarized surface states and employ a Wannier-based scheme for the spin-flip matrix elements. We find that the spin-flip excitations associated with the surface states exhibit an important angular modulation which is completely absent in the standard Rashba model rashba. Furthermore, we demonstrate that the maximum of the calculated spin-flip absorption rate is about twice the model prediction. These results show that although the Rashba model accurately describes the spectrum and spin polarization, it does not fully account for the dynamical properties of the surface states.