RESUMEN
We report on the epitaxial fabrication and electronic properties of a topological phase in strained α-Sn on InSb. The topological surface state forms in the presence of an unusual band order not based on direct spin-orbit coupling, as shown in density functional and GW slab-layer calculations. Angle-resolved photoemission including spin detection probes experimentally how the topological spin-polarized state emerges from the second bulk valence band. Moreover, we demonstrate the precise control of the Fermi level by dopants.
RESUMEN
The helical Dirac fermions at the surface of topological insulators show a strong circular dichroism which has been explained as being due to either the initial-state spin angular momentum, the initial-state orbital angular momentum, or the handedness of the experimental setup. All of these interpretations conflict with our data from Bi(2)Te(3) which depend on the photon energy and show several sign changes. Our one-step photoemission calculations coupled to ab initio theory confirm the sign change and assign the dichroism to a final-state effect. Instead, the spin polarization of the photoelectrons excited with linearly polarized light remains a reliable probe for the spin in the initial state.
RESUMEN
Graphene in spintronics is predominantly considered for spin current leads of high performance due to weak intrinsic spin-orbit coupling of the graphene π electrons. Externally induced large spin-orbit coupling opens the possibility of using graphene in active elements of spintronic devices such as the Das-Datta spin field-effect transistor. Here we show that Au intercalation at the graphene-Ni interface creates a giant spin-orbit splitting (~100 meV) of the graphene Dirac cone up to the Fermi energy. Photoelectron spectroscopy reveals the hybridization with Au 5d states as the source for this giant splitting. An ab initio model of the system shows a Rashba-split spectrum around the Dirac point of graphene. A sharp graphene-Au interface at the equilibrium distance accounts for only ~10 meV spin-orbit splitting and enhancement is due to the Au atoms in the hollow position that get closer to graphene and do not break the sublattice symmetry.
RESUMEN
We study the effect of Fe impurities deposited on the surface of the topological insulator Bi(2)Se(3) by means of core-level and angle-resolved photoelectron spectroscopy. The topological surface state reveals surface electron doping when the Fe is deposited at room temperature and hole doping with increased linearity when deposited at low temperature (~8 K). We show that in both cases the surface state remains intact and gapless, in contradiction to current belief. Our results suggest that the surface state can very well exist at functional interfaces with ferromagnets in future devices.
RESUMEN
We reveal a giant Rashba effect (α(R)≈1.3 eV Å) on a surface state of Ir(111) by angle-resolved photoemission and by density functional theory. It is demonstrated that the existence of the surface state, its spin polarization, and the size of its Rashba-type spin-orbit splitting remain unaffected when Ir is covered with graphene. The graphene protection is, in turn, sufficient for the spin-split surface state to survive in ambient atmosphere. We discuss this result along with indications for a topological protection of the surface state.
RESUMEN
The spectral weight evolution of the low-dimensional Mott insulator TiOCl upon alkali-metal dosing has been studied by photoelectron spectroscopy. We observe a spectral weight transfer between the lower Hubbard band and an additional peak upon electron doping, in line with quantitative expectations in the atomic limit for changing the number of singly and doubly occupied sites. This observation is an unconditional hallmark of correlated bands and has not been reported before. In contrast, the absence of a metallic quasiparticle peak can be traced back to a simple one-particle effect.
RESUMEN
The effects of total parenteral nutrition (TPN) versus enteral nutrition (TEN) were studied in 34 patients following major neurosurgery. Measurements were made of resting energy expenditure (REE), urea production rate (UPR), visceral proteins, parameters of liver and pancreas function, as well as gastrointestinal absorption. To predict nutritional status, nutritional index (NI) was calculated. UPR revealed no significant differences between the groups. After 12 days of TEN, however, synthesis of visceral proteins increased significantly. In addition, NI improved after TEN (p < 0.05), whereas it remained unchanged after TPN. Thrombocyte and lymphocyte counts rose predominately during enteral nutrition. Only in the TEN group was REE increased by 18% and Glasgow Coma Scale (GCS) enhanced from Day 6 on. Exogenous insulin demand was enhanced in the parenterally fed group, and bilirubin (p < 0.05), amylase (p < 0.05), and lipase (p < 0.01) rose significantly, as did gamma-glutamyl-transferase (p < 0.0005) and alkaline phosphatase (p < 0.0005). After 12 d of TPN, vitamin A absorption was significantly attenuated, indicating reduced fat absorption compared to TEN. Carbohydrate absorption did not show significant changes between the groups. Only during TPN did mean values of xylose absorption remain below the normal range. Therefore, enteral nutrition following neurosurgical procedures is associated with an accelerated normalization of nutritional status and an improved substrate tolerance. TEN opposes early postoperative absorption disturbances of the small intestine.
