Rashba Spin-Orbit Coupling in Image Potential States.

The search in two-dimensional condensed matter systems of Rashba-type spin-polarized electronic states is aimed by the possibility to control and manipulate the spin orientation. In this Letter, for the first time, we report on the experimental evidence of a Rashba-type spin splitting in the n=1 image potential state. The image potential state Rashba splitting here measured at the graphene/Ir(111) interface, as confirmed by theoretical considerations, can be detectable to any metal surface with a significant spin-orbit coupling.

Spin polarized metastable helium de-excitation processes on metal surfaces.

Spin polarized de-excitation of a metastable helium atom interacting with metal surfaces is treated within density functional theory. The method is based on a self-consistent calculation of the spin dependent electronic properties of the system, such as the surface density of states and the localized surface states, to compute the transition rate. On the high work function Ag(100) and Ag(111) surfaces, the helium 2s electron is delocalized in the metal and hence the transition rate is weakly spin dependent. The existence of a Shockley surface state in Ag(111) determines a neutralization rate that is about 59% larger than that from Ag(100). On a low work function metal, namely Na(100), the rate is of smaller magnitude than those on silver because the 2s triplet resonance is found to be more occupied. Consequently, emitted electrons can display a strong spin dependence also for a paramagnetic surface.

Bi ordered phases on Cu(100): periodic arrays of dislocations influence the electronic properties.

A single layer of bismuth deposited on the Cu(100) surface forms long range ordered structural phases at various Bi density. A highly ordered c(2 x 2) reconstruction is accomplished at 0.5 ML, further Bi deposition induces a c(9square root of 2 x square root of 2)R45 degrees structure and a subsequent p(10 x 10) phase related to the formation of regular dislocations arrays. The transition from a c(2 x 2) superstructure to the c(9square root of 2 x square root of 2)R45 degrees phase is accompanied by a sudden decrease in the work function. Photoemission measurements reveal that the Bi induced states close to the Fermi level, associated to the c(2 x 2) phase, are strongly quenched when the arrays of dislocations are formed, while at higher binding energies, they undergo an energy shift probably due to a confinement effect. The low-energy single particle excitations and the electron dispersion of the Bi induced states of the c(2 x 2) phase are compared to the electronic states deduced by theoretical band structure obtained by ab initio calculation performed within the embedding method applied to a realistic semi-infinite system.

Dynamics of electron distributions probed by helium scattering.

Helium atom scattering (HAS) is the most important tool for surface science investigations. The analysis of helium scattering off a solid surface allows for a detailed analysis of its structural and dynamical properties. In this work we show how the dynamics of electron distributions at a metal surface can be investigated by HAS in the adiabatic approximation. First we examine the anticorrugating effect, namely the property of the He-surface potential of those metal systems in which the classical turning points of He beams are farther away from the surface layer at the bridge than at top sites. Anticorrugation for the system He/Cu(111) is examined in detail by a density functional theory (DFT) calculation and compared with the corrugating behaviour of He/Al(111). To explain such an effect the charge polarization of the system is crucial. Second we consider theoretically a surprising restricted diffusion result in the normal direction for Na adatoms on Cu(001) at coverages larger than 0.04 ML, obtained by measurements with spin polarized (3)He beams. From DFT calculations for this system a model for the description of the He-surface interaction based on the effective medium theory, which accounts for the observed phenomenon, is discussed. We show that the surface charge distribution probed by HAS is altered by the local concentration of the diffusing adatoms which is fluctuating with time and producing variations in the apparent height of the adatom measured by HAS. Our calculations demonstrate that such electronic dynamical rearrangements can be probed by the (3)He spin echo technique, which could be extended to other studies of surface electronic properties.