Wednesday, July 17, 2013

Clarifying the "Rashba" effect

At the conference today Changyoung Kim gave a nice talk about how the "Rashba effect" [coupling of momentum and spin] on the surface of a semiconductor has a different physical origin to what is usually claimed. In particular, the energy scale for the relativistic Zeeman splitting proposed by Rashba gives a band splitting that is six orders of magnitude smaller than what is actually observed!

Here is the abstract of the associated PRL:
We propose that the existence of local orbital angular momentum (OAM) on the surfaces of high-Z materials plays a crucial role in the formation of Rashba-type surface band splitting. Local OAM state in a Bloch wave function produces an asymmetric charge distribution (electric dipole). The surface-normal electric field then aligns the electric dipole and results in chiral OAM states and the relevant Rashba-type splitting. Therefore, the band splitting originates from electric dipole interaction, not from the relativistic Zeeman splitting as proposed in the original Rashba picture. The characteristic spin chiral structure of Rashba states is formed through the spin-orbit coupling and thus is a secondary effect to the chiral OAM. 


  1. Thanks for this reference. I recently did a few spin polarized photoemission experiments on the Au(111) surface state for calibration purposes, but I did not realize this huge quantitative discrepancy!

  2. Well, this point is made very clear in Ronald Winkler's book (Ch. 6)...