Spin-polarized electrons confined in low-dimensional structures are of high interest for spintronics applications. Here, we investigate the electronic structure of an ordered array of Bi monomer and dimer chains on the Ag(110) surface. By means of spin-resolved photoemission spectroscopy, we find Rashba-Bychkov split bands crossing the Fermi level with one-dimensional constant energy contours. These bands are up-spin polarized for positive wave vectors and down-spin polarized for negative wave vectors, at variance with the Rashba-Bychkov model that predicts a pair of states with opposite spin in each half of the surface Brillouin zone. Density functional theory shows that spin-selective hybridization with the Ag bulk bands originates this unconventional spin texture.

Two-dimensional superconductivity in alkali- and alkaline-Earth-metal doped monolayer graphene has been explained in the framework of electron-phonon coupling (EPC) and experiments yielded superconducting transition temperatures (T C ) up to 6 K. In contrast to bulk graphite intercalation compounds, the interface of doped graphene with its environment affects its physical properties. Here we present a novel and well-defined BaC8 interface structure in Ba-doped single-layer graphene on Au and Ge substrates. We use angle-resolved photoemission spectroscopy in combination with ab initio modelling to extract the Eliashberg function and EPC for both substrates. This allows us to quantitatively assess the environmental effects for both Au and Ge substrates on superconductivity in graphene. We show that for semiconducting Ge substrates, the doping level and EPC are higher. Our study highlights that both dopant order and the metallicity of the substrate can be used to control EPC and hence superconductivity.

ARPES is a priori a technique of choice to measure the Fermi velocities v(F) in metals. In correlated systems, it is interesting to compare this experimental value to that obtained in band structure calculations, as deviations are usually taken as a good indicator of the presence of strong electronic correlations. Nevertheless, it is not always straightforward to extract v(F) from ARPES spectra. We study here the case of layered cobaltates, an interesting family of correlated metals. We compare the results obtained by standard methods, namely the fit of spectra at constant momentum k (energy distribution curve, EDC) or constant binding energy omega (momentum distribution curve, MDC). We find that the difference of v(F) between the two methods can be as large as a factor 2. The reliability of the 2 methods is intimately linked to the degree of k- and omega-dependence of the electronic self-energy. As the k-dependence is usually much smaller than the omega dependence for a correlated system, the MDC analysis is generally expected to give more reliable results. However, we review here several examples within cobaltates, where the MDC analysis apparently leads to unphysical results, while the EDC analysis appears coherent. We attribute the difference between the EDC and MDC analysis to a strong variation of the photoemission intensity with the momentum k. This distorts the MDC lineshapes but does not affect the EDC ones. Simulations including a k dependence of the intensity allow to reproduce the difference between MDC and EDC analysis very well. This momentum dependence could be of extrinsic or intrinsic. We argue that the latter is the most likely and actually contains valuable information on the nature of the correlations that would be interesting to extract further. (c) 2012 Elsevier B.V. All rights reserved.