167 research outputs found
Combined large spin splitting and one-dimensional confinement in surface alloys
We have found and characterized by angle-resolved photoelectron spectroscopy
(ARPES) quasi-one dimensional spin-split states in chain-like surface alloys
formed by large Z elements (Bi and Pb) at the Cu(110) surface. The ARPES
results are supported by first-principles relativistic calculations, which also
confirm the spin polarization of these states, characteristic of the
Rashba-Bychkov effect. The Fermi surface contours are open, but warped, as a
result of the interaction with the bulk Cu conduction band. This interaction
introduces a k dependence of the spin splitting perpendicular to the chains
direction. We have also investigated the influence of the atomic spin-orbit
parameter in substitutional isostructural Bi_{1-x}Pb_{x} overlayers, and found
that the magnitude of the spin splitting can be continuously tuned as a
function of stoichiometry.Comment: 8 pages, 4 figure
Diversity of radial spin textures in chiral materials
We introduce a classification of the radial spin textures in momentum space that emerge at the high-symmetry points in crystals characterized by nonpolar chiral point groups (D2, D3, D4, D6, T , O). Based on the symmetry constraints imposed by these point groups in a vector field, we study the general expression for the radial spin textures up to third order in momentum. Furthermore, we determine the high-symmetry points of the 45 nonpolar chiral space groups supporting a radial spin texture. These two principles are used to screen materials databases for archetypes that go beyond the basic hedgehog radial spin texture. Among the selected materials we highlight the axion insulator candidate Ta2Se8I, the material proposed for dark matter detection Ag3AuTe2, and heazlewoodite Ni3S2, a conventional metal predicted to exhibit current-induced spin polarization. We point out that the symmetry analysis proposed in this Letter is more general and extends to studying other vector properties in momentum space.D.G.-M. and O.V.Y. acknowledge support by the NCCR MARVEL, a National Centre of Competence in Research, funded by the Swiss National Science Foundation (Grant No. 182892). First-principles calculations were performed at the Swiss National Supercomputing Centre (CSCS) under Project No. s1146. D.G.-M. thanks the MarĂa Zambrano Programme at the University of Alicante founded by the European Union-Next Generation EU as well as J. J. Palacios for insightful discussions. This study forms part of the Advanced Materials program and was supported by the Spanish MCIN with funding from European Union Next Generation EU and by Generalitat Valenciana (Grant No. MFA/2022/045)
Anisotropic spin gaps in BiAg-Ag/Si(111)
We present a detailed analysis of the band structure of the
BiAg/Ag/Si(111) trilayer system by means of high resolution Angle Resolved
Photoemission Spectroscopy (ARPES). BiAg2/Ag/Si(111) exhibits a complex spin
polarized electronic structure due to giant spin-orbit interactions. We show
that a complete set of constant energy ARPES maps, supplemented by a modified
nearly free electron calculation, provides a unique insight into the structure
of the spin polarized bands and spin gaps. We also show that the complex gap
structure can be continuously tuned in energy by a controlled deposition of an
alkali metal.Comment: 6 pages, 5 figure
Statins, antihypertensive treatment, and blood pressure control in clinic and over 24 hours: evidence from PHYLLIS randomised double blind trial
Objective To investigate the possibility that statins reduce blood pressure as well as cholesterol concentrations through clinic and 24 hour ambulatory blood pressure monitoring
Ramifications of Optical Pumping on the Interpretation of Time-Resolved Photoemission Experiments on Graphene
In pump-probe time and angle-resolved photoemission spectroscopy (TR-ARPES)
experiments the presence of the pump pulse adds a new level of complexity to
the photoemission process in comparison to conventional ARPES. This is
evidenced by pump-induced vacuum space-charge effects and surface
photovoltages, as well as multiple pump excitations due to internal reflections
in the sample-substrate system. These processes can severely affect a correct
interpretation of the data by masking the out-of-equilibrium electron dynamics
intrinsic to the sample. In this study, we show that such effects indeed
influence TR-ARPES data of graphene on a silicon carbide (SiC) substrate. In
particular, we find a time- and laser fluence-dependent spectral shift and
broadening of the acquired spectra, and unambiguously show the presence of a
double pump excitation. The dynamics of these effects is slower than the
electron dynamics in the graphene sample, thereby permitting us to deconvolve
the signals in the time domain. Our results demonstrate that complex
pump-related processes should always be considered in the experimental setup
and data analysis.Comment: 9 pages, 4 figure
Ultrafast Dynamics of Massive Dirac Fermions in Bilayer Graphene
Bilayer graphene is a highly promising material for electronic and
optoelectronic applications since it is supporting massive Dirac fermions with
a tuneable band gap. However, no consistent picture of the gap's effect on the
optical and transport behavior has emerged so far, and it has been proposed
that the insulating nature of the gap could be compromised by unavoidable
structural defects, by topological in-gap states, or that the electronic
structure could be altogether changed by many-body effects. Here we directly
follow the excited carriers in bilayer graphene on a femtosecond time scale,
using ultrafast time- and angle-resolved photoemission. We find a behavior
consistent with a single-particle band gap. Compared to monolayer graphene, the
existence of this band gap leads to an increased carrier lifetime in the
minimum of the lowest conduction band. This is in sharp contrast to the second
sub-state of the conduction band, in which the excited electrons decay through
fast, phonon-assisted inter-band transitions.Comment: 5 pages, 4 figure
Disentangling thermal and nonthermal excited states in a charge-transfer insulator by time- and frequency-resolved pump-probe spectroscopy
Time- and frequency-resolved pump-probe optical spectroscopy is used to investigate the effects of the impulsive injection of delocalized excitations through a charge-transfer process in insulating CuGeO3. A large broadening of the charge-transfer edge is observed on the sub-ps time scale. The modification of this spectral feature cannot be attributed to the local increase in the effective temperature, as a consequence of the energy absorbed by the pump pulse. The measured modifications of the optical properties of the system are consistent with the creation of a nonthermal state, metastable on the picosecond time scale, after the pump-induced impulsive modification of the electron interactions
Two-Dimensional and Three-Dimensional Biomechanical Factors During 90° Change of Direction are Associated to Non-Contact ACL injury in Female Soccer Players
# Background
The two-dimensional (2D) video-analysis of the change of direction (COD) technique has never been used to attempt to predict the risk of ACL injury in female football players.
# Hypothesis/Purpose
The purpose of the present pilot study was to prospectively investigate the biomechanical predictors of ACL injury during a COD task in female football players using both gold standard 3D motion capture and a qualitative scoring system based on 2D video-analysis.
# Study Design
Prospective cohort study
# Methods
Sixteen competitive female football (soccer) players (age 21.4 ± 4.3) performed a series of pre-planned 90° COD tasks. 3D motion data was recorded through 10 stereophotogrammetric cameras and a force platform. 2D frontal and transverse plane joint kinematics were computed through video-analysis from three high-speed cameras. A scoring system based on five criteria was adopted: limb stability, pelvis stability, trunk stability, shock absorption, and movement strategy. The players were prospectively followed for the next two consecutive football seasons and the occurrence of severe knee injuries was registered.
# Results
Four players (25%) experienced an ACL injury. In 3D analysis, ACL-injured players showed greater knee valgus, knee internal rotation, and lower knee flexion (p= 0.017 -- 0.029). Lower hip flexion coupled with greater external rotation (p= 0.003 -- 0.042), ankle eversion, and contralateral pelvic drop (p\<0.001) were also noted. In 2D analysis, ACL-injured players showed greater internal foot rotation, contralateral pelvic drop, lower knee flexion, and contralateral trunk tilt (moderate-to-large effect size). Pelvis stability and trunk stability showed the highest predictive value towards ACL injury. Total score was significantly lower in ACL-injured players with a moderate effect size (d=0.45).
# Conclusions
Both 3D and 2D methodologies depicted biomechanical risk factors and offered predictive insights towards the ACL injury risk. Awareness should rise in women's football regarding the high risk of ACL injury and the strategies to assess and mitigate it.
# Level of Evidence
3
©The Author(s
Direct view on the ultrafast carrier dynamics in graphene
The ultrafast dynamics of excited carriers in graphene is closely linked to
the Dirac spectrum and plays a central role for many electronic and
optoelectronic applications. Harvesting energy from excited electron-hole
pairs, for instance, is only possible if these pairs can be separated before
they lose energy to vibrations, merely heating the lattice. While the hot
carrier dynamics in graphene could so far only be accessed indirectly, we here
present a direct time-resolved view on the Dirac cone by angle-resolved
photoemission (ARPES). This allows us to show the quasi-instant thermalisation
of the electron gas to a temperature of more than 2000 K; to determine the
time-resolved carrier density; to disentangle the subsequent decay into
excitations of optical phonons and acoustic phonons (directly and via
supercollisions); and to show how the presence of the hot carrier distribution
affects the lifetime of the states far below the Fermi energy.Comment: 15 pages, 4 figure
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