349 research outputs found
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
Autonomous Shuttle Implementation and Best Practices
When, where, and how autonomous shuttles are deployed can have significant safety, economic, and policy impacts on their operation and performance. This research analyzes data related to 120 existing deployments of autonomous shuttles, looking at safety, operational, economic, and policy-related issues. Analysis shows that autonomous shuttles would be an excellent supplement to public transportation. However, improvements to the vehicle and the infrastructure are needed before any permanent deployment. The study also analyzes the perceptions of practitioners, industry experts, and transportation system users toward autonomous shuttles. Principal Component Analysis (PCA) and Multiple Input Multiple Cause Structural Equation Modelling (SEM) approaches were adopted to analyze the perception data. The results from the PCA highlighted critical barriers to autonomous shuttle implementation, including underutilization measures, safety concerns, seating arrangements, reliability, data security, operational aspects, sensor technology, and lane use. The results from the SEM revealed that users’ willingness to use autonomous shuttles is influenced by their perceived safety, comfort, trust in autonomous shuttles, familiarity with autonomous shuttles, household income, age, and frequency of transit usage. A set of recommended best practices for deploying autonomous shuttles is proposed based on the insights from multiple case studies and the perceptions of practitioners and industry experts
A Real-Time Comparison of Four Particulate Matter Size Fractions in the Personal Breathing Zone of Paris Subway Workers: A Six-Week Prospective Study.
We developed a Bayesian spline model for real-time mass concentrations of particulate matter (PM10, PM2.5, PM1, and PM0.3) measured simultaneously in the personal breathing zone of Parisian subway workers. The measurements were performed by GRIMM, a gravimetric method, and DiSCmini during the workers' work shifts over two consecutive weeks. The measured PM concentrations were analyzed with respect to the working environment, the underground station, and any specific events that occurred during the work shift. Overall, PM0.3 concentrations were more than an order of magnitude lower compared to the other PM concentrations and showed the highest temporal variation. The PM2.5 levels raised the highest exposure concern: 15 stations out of 37 had higher mass concentrations compared to the reference. Station PM levels were not correlated with the annual number of passengers entering the station, the year of station opening or renovation, or the number of platforms and tracks. The correlation with the number of station entrances was consistently negative for all PM sizes, whereas the number of correspondence concourses was negatively correlated with PM0.3 and PM10 levels and positively correlated with PM1 and PM2.5 levels. The highest PM10 exposure was observed for the station platform, followed by the subway cabin and train, while ticket counters had the highest PM0.3, PM1, and PM2.5 mass concentrations. We further found that compared to gravimetric and DiSCmini measurements, GRIMM results showed some discrepancies, with an underestimation of exposure levels. Therefore, we suggest using GRIMM, calibrated by gravimetric methods, for PM sizes above 1μm, and DiSCmini for sizes below 700 nm
Tuning independently Fermi energy and spin splitting in Rashba systems: Ternary surface alloys on Ag(111)
By detailed first-principles calculations we show that the Fermi energy and
the Rashba splitting in disordered ternary surface alloys (BiPbSb)/Ag(111) can
be independently tuned by choosing the concentrations of Bi and Pb. The
findings are explained by three fundamental mechanisms, namely the relaxation
of the adatoms, the strength of the atomic spin-orbit coupling, and band
filling. By mapping the Rashba characteristics,i.e.the splitting and the Rashba
energy, and the Fermi energy of the surface states in the complete range of
concentrations. Our results suggest to investigate experimentally effects which
rely on the Rashba spin-orbit coupling in dependence on spin-orbit splitting
and band filling.Comment: 11 pages, 3 figure
Universal response of the type-II Weyl semimetals phase diagram
The discovery of Weyl semimetals represents a significant advance in
topological band theory. They paradigmatically enlarged the classification of
topological materials to gapless systems while simultaneously providing
experimental evidence for the long-sought Weyl fermions. Beyond fundamental
relevance, their high mobility, strong magnetoresistance, and the possible
existence of even more exotic effects, such as the chiral anomaly, make Weyl
semimetals a promising platform to develop radically new technology. Fully
exploiting their potential requires going beyond the mere identification of
materials and calls for a detailed characterization of their functional
response, which is severely complicated by the coexistence of surface- and
bulk-derived topologically protected quasiparticles, i.e., Fermi arcs and Weyl
points, respectively. Here, we focus on the type-II Weyl semimetal class where
we find a stoichiometry-dependent phase transition from a trivial to a
non-trivial regime. By exploring the two extreme cases of the phase diagram, we
demonstrate the existence of a universal response of both surface and bulk
states to perturbations. We show that quasi-particle interference patterns
originate from scattering events among surface arcs. Analysis reveals that
topologically non-trivial contributions are strongly suppressed by spin
texture. We also show that scattering at localized impurities generate
defect-induced quasiparticles sitting close to the Weyl point energy. These
give rise to strong peaks in the local density of states, which lift the Weyl
node significantly altering the pristine low-energy Weyl spectrum. Visualizing
the microscopic response to scattering has important consequences for
understanding the unusual transport properties of this class of materials.
Overall, our observations provide a unifying picture of the Weyl phase diagram
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