We present the first spin-resolved inverse-photoemission measurements of the unoccupied part of the Rashba-split surface state on Au(111). This Shockley-type state is considered as the prototype of a Rashba-split electron state on a metallic surface. The spin splitting of the occupied part of this state was first indicated by spin-integrated photoemission data [1]. This pioneering work was followed by a spin-resolved study, which directly proved the spin structure of the state [2].

 

Our study complements the information on the spin character by following the surface state into the unoccupied energy region. The state crosses the Fermi energy as a function of the wave vector parallel to the surface and finally leaves the bulk-band energy gap. Our spin-resolved inverse-photoemission experiment stands out from conventional systems thanks to an improved energy and k resolution [3]. Our data confirm the spin character of the surface state, as far as it does not overlap with bulk states. In addition, we show how the spin character is altered when the surface state becomes degenerate with bulk states.

 

Further Rashba systems with even larger spin splittings as well as topological insulators are currently investigated with our spin-resolved inverse-photoemission apparatus. We will provide a status report on our latest results.

 

[1] LaShell et al., Phys. Rev. Lett. 77, 3419 (1996)

[2] Hoesch et al., Phys. Rev. B 69, 241401(R) (2004)

[3] Budke et al., Rev. Sci. Instrum. 78, 083903 (2007)