452 research outputs found
Spin- and angle-resolved photoemission on topological materials
A historical review of spin- and angle-resolved photoemission on topological
materials is presented, aimed at readers who are new to the field or who wish
to obtain an overview of the activities in the field. The main focus lies on
topological insulators, but also Weyl and other semimetals will be discussed.
Further it will be explained why the measured spin polarisation from a spin
polarised state should always add up to 100% and how spin interference effects
influence the measured spin texture.Comment: Invited review article for special issue "ARPES Studies of
Topological Materials" in Electronic Structur
Determination of the time scale of photoemission from the measurement of spin polarization
The Eisenbud-Wigner-Smith (EWS) time delay of photoemission depends on the
phase term of the matrix element describing the transition. Because of an
interference process between partial channels, the photoelectrons acquire a
spin polarization which is also related to the phase term. The analytical model
for estimating the time delay by measuring the spin polarization is reviewed in
this manuscript. In particular, the distinction between scattering EWS and
interfering EWS time delay will be introduced, providing an insight in the
chronoscopy of photoemission. The method is applied to the recent experimental
data for Cu(111) presented in M. Fanciulli et al., PRL 118, 067402 (2017),
allowing to give better upper and lower bounds and estimates for the EWS time
delays.Comment: 30 pages, 5 figure
Tuning of the Rashba effect in Pb quantum well states via a variable Schottky barrier
Spin-orbit interaction (SOI) in low-dimensional systems results in the
fascinating property of spin-momentum locking. In a Rashba system the inversion
symmetry normal to the plane of a two-dimensional (2D) electron gas is broken,
generating a Fermi surface spin texture reminiscent of spin vortices of
different radii. This can be exploited in a spin-based field-effect transistor
(spin- FET), where the Rashba system forms a 2D channel between ferromagnetic
(FM) source and drain electrodes. The electron spin precesses when propagating
through the Rashba channel and spin orientations (anti)parallel to the drain
give (low) high conductivity. Crucial is the possibility to tune the momentum
splitting, and consequently the precession angle, through an external
parameter. Here we show that this can be achieved in Pb quantum well states
through the doping dependence of the Schottky barrier, opening up the
possibility of a terahertz spin-FET.Comment: 8 pages, 7 figure
Controlling the effective mass of quantum well states in Pb/Si(111) by interface engineering
The in-plane effective mass of quantum well states in thin Pb films on a Bi
reconstructed Si(111) surface is studied by angle-resolved photoemission
spectroscopy. It is found that this effective mass is a factor of three lower
than the unusually high values reported for Pb films grown on a Pb
reconstructed Si(111) surface. Through a quantitative low-energy electron
diffraction analysis the change in effective mass as a function of coverage and
for the different interfaces is linked to a change of around 2% in the in-plane
lattice constant. To corroborate this correlation, density functional theory
calculations were performed on freestanding Pb slabs with different in-plane
lattice constants. These calculations show an anomalous dependence of the
effective mass on the lattice constant including a change of sign for values
close to the lattice constant of Si(111). This unexpected relation is due to a
combination of reduced orbital overlap of the 6p_z states and altered
hybridization between the 6p_z and 6p_xy derived quantum well states.
Furthermore it is shown by core level spectroscopy that the Pb films are
structurally and temporally stable at temperatures below 100 K.Comment: 7 pages, 6 figure
Evolutionary analysis of the lysine-rich N-terminal cytoplasmic domains of the gastric H+,K+-ATPase and the Na+,K+-ATPase
The catalytic α-subunits of both the Na+,K+-ATPase and the gastric H+,K+-ATPase possess lysine-rich N-termini which project into the cytoplasm. Due to conflicting experimental results it is currently unclear whether the N-termini play a role in ion pump function or regulation, and, if they do, by what mechanism. Comparison of the lysine frequencies of the N-termini of both proteins with those of all of their extramembrane domains showed that the N-terminal lysine frequencies are far higher than one would expect simply from exposure to the aqueous solvent. The lysine frequency was found to vary significantly between different vertebrate classes, but this is due predominantly to a change in N-terminal length. As evidenced by a comparison between fish and mammals, an evolutionary trend towards an increase of the length of the N-terminus of the H+,K+-ATPase on going from an ancestral fish to mammals could be identified. This evolutionary trend supports the hypothesis that the N-terminus is important in ion pump function or regulation. In placental mammals, one of the lysines is replaced by serine (Ser-27), which is a target for protein kinase C. In most other animal species a lysine occupies this position and hence no protein kinase C target is present. Interaction with protein kinase C is thus not the primary role of the lysine-rich N-terminus. The disordered structure of the N-terminus may, via increased flexibility, facilitate interaction with another binding partner, e.g. the surrounding membrane, or help to stabilize particular enzyme conformations via the increased entropy it produces.Australian Research Counci
Observation of correlated spin-orbit order in a strongly anisotropic quantum wire system
Quantum wires with spin-orbit coupling provide a unique opportunity to
simultaneously control the coupling strength and the screened Coulomb
interactions where new exotic phases of matter can be explored. Here we report
on the observation of an exotic spin-orbit density wave in Pb-atomic wires on
Si(557) surfaces by mapping out the evolution of the modulated spin-texture at
various conditions with spin- and angle-resolved photoelectron spectroscopy.
The results are independently quantified by surface transport measurements. The
spin polarization, coherence length, spin dephasing rate, and the associated
quasiparticle gap decrease simultaneously as the screened Coulomb interaction
decreases with increasing excess coverage, providing a new mechanism for
generating and manipulating a spin-orbit entanglement effect via electronic
interaction. Despite clear evidence of spontaneous spin-rotation symmetry
breaking and modulation of spin-momentum structure as a function of excess
coverage, the average spin-polarization over the Brillouin zone vanishes,
indicating that time-reversal symmetry is intact as theoretically predicted
Conformational isomers of stilbene on Si(1 0 0)
Stilbene (1,2-diphenylethylene) has shown an intriguing isomerisation behavior and may serve as a model system for “molecular switches” incorporating a CC double bond. To evaluate the possible use of such molecules as molecular switches on semiconductor surfaces, the adsorption of cis- and trans-stilbene on Si(1 0 0) has been investigated. Identification of both isomers is achieved by differences in adsorption geometry as revealed by NEXAFS, and differences in electronic structure in the occupied and unoccupied molecular orbitals. For both isomers, bonding takes place via the CC double bond to the Si dimer atoms allowing for free movement of the aromatic rings, a necessary prerequisite for photoinduced isomerisation on the surface. Our experimental results agree well with theoretical calculations
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