693 research outputs found
Quantum states and linear response in dc and electromagnetic fields for charge current and spin polarization of electrons at Bi/Si interface with giant spin-orbit coupling
An expansion of the nearly free-electron model constructed by Frantzeskakis,
Pons and Grioni [Phys. Rev. B {\bf 82}, 085440 (2010)] describing quantum
states at Bi/Si(111) interface with giant spin-orbit coupling is developed and
applied for the band structure and spin polarization calculation, as well as
for the linear response analysis for charge current and induced spin caused by
dc field and by electromagnetic radiation. It is found that the large
spin-orbit coupling in this system may allow resolving the spin-dependent
properties even at room temperature and at realistic collision rate. The
geometry of the atomic lattice combined with spin-orbit coupling leads to an
anisotropic response both for current and spin components related to the
orientation of the external field. The in-plane dc electric field produces only
the in-plane components of spin in the sample while both the in-plane and
out-of-plane spin components can be excited by normally propagating
electromagnetic wave with different polarizations.Comment: 10 pages, 9 figure
Constructing a Large Variety of Dirac-Cone Materials in the BiSb Thin Film System
We theoretically predict that a large variety of Dirac-cone materials can be
constructed in BiSb thin films, and we here show how to
construct single-, bi- and tri- Dirac-cone materials with various amounts of
wave vector anisotropy. These different types of Dirac cones can be of special
interest to electronic devices design, quantum electrodynamics and other
fields
Low energy high angular resolution neutral atom detection by means of micro-shuttering techniques: the BepiColombo SERENA/ELENA sensor
The neutral sensor ELENA (Emitted Low-Energy Neutral Atoms) for the ESA
cornerstone BepiColombo mission to Mercury (in the SERENA instrument package)
is a new kind of low energetic neutral atoms instrument, mostly devoted to
sputtering emission from planetary surfaces, from E ~20 eV up to E~5 keV,
within 1-D (2x76 deg). ELENA is a Time-of-Flight (TOF) system, based on
oscillating shutter (operated at frequencies up to a 100 kHz) and mechanical
gratings: the incoming neutral particles directly impinge upon the entrance
with a definite timing (START) and arrive to a STOP detector after a flight
path. After a brief dissertation on the achievable scientific objectives, this
paper describes the instrument, with the new design techniques approached for
the neutral particles identification and the nano-techniques used for designing
and manufacturing the nano-structure shuttering core of the ELENA sensor. The
expected count-rates, based on the Hermean environment features, are shortly
presented and discussed. Such design technologies could be fruitfully exported
to different applications for planetary exploration.Comment: 11 page
Molecular Line Observations of a Carbon-Chain-Rich Core L492
We report on molecular abundances and distributions in a starless dense core
L492. We have found that the abundances of carbon-chain molecules such as CCS,
CS, HCN, HCN, and HCN are comparable to those in
chemically young dark cloud cores called "carbon-chain--producing regions",
such as L1495B, L1521B, L1521E, and TMC-1. This is the first dark cloud core
with extremely rich in carbon-chain-molecules that is found outside the Taurus
region. In addition, the deuterium fractionation ratios of DNC/HNC and
DCO/HCO are also comparable to those in carbon-chain--producing
regions, being significantly lower than those in the evolved prestellar cores
such as L1498 and L1544. On the other hand, the abundances of NH and
NH are systematically higher than those in carbon-chain--producing
regions. Our mapping observations reveal that the central hole of molecular
distributions, which were reported for CCS and CS in evolved prestellar
cores is not significant in L492, indicating that the depletion factor of
molecules is not very high. Furthermore, L492 is dynamically more evolved than
carbon-chain--producing regions, and the protostellar collapse has started like
L1498 and L1544. Therefore, it is likely that the chemical and dynamical
evolutionary stage of L492 is intermediate between carbon-chain--producing
regions (L1495B, L1521B, L1521E, and TMC-1) and evolved prestellar cores (L1498
and L1544).Comment: 26 pages, 8 figures, accepted for publication in The Astrophysical
Journal (Preprint with high resolution figures will be available at
http://www.nro.nao.ac.jp/library/report/list.html
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Estimating sea surface temperature measurement methods using characteristic differences in the diurnal cycle
Lack of reliable observational metadata represents a key barrier to understanding sea surface temperature (SST) measurement biases, a large contributor to uncertainty in the global surface record. We present a method to identify SST measurement practice by comparing the observed SST diurnal cycle from individual ships with a reference from drifting buoys under similar conditions of wind and solar radiation. Compared to existing estimates, we found a larger number of engine room-intake (ERI) reports post War World II and in the period 1960 â 1980. Differences in the inferred mixture of observations lead to a systematic warmer shift of the bias adjusted SST anomalies from 1980 compared to previous estimates, while reducing the ensemble spread. Changes in mean field differences between bucket and ERI SST anomalies in the Northern Hemisphere over the period 1955 â 1995 could be as large as 0.5 °C and are not well reproduced by current bias adjustment models
On the diffraction pattern of C60 peapods
We present detailed calculations of the diffraction pattern of a powder of
bundles of C peapods. The influence of all pertinent structural
parameters of the bundles on the diffraction diagram is discussed, which should
lead to a better interpretation of X-ray and neutron diffraction diagrams. We
illustrate our formalism for X-ray scattering experiments performed on peapod
samples synthesized from 2 different technics, which present different
structural parameters. We propose and test different criteria to solve the
difficult problem of the filling rate determination.Comment: Sumitted 19 May 200
On the Influence of Uncertainties in Chemical Reaction Rates on Results of the Astrochemical Modelling
With the chemical reaction rate database UMIST95 (Millar et al. 1997) we
analyze how uncertainties in rate constants of gas-phase chemical reactions
influence the modelling of molecular abundances in the interstellar medium.
Random variations are introduced into the rate constants to estimate the
scatter in theoretical abundances. Calculations are performed for dark and
translucent molecular clouds where gas phase chemistry is adequate. Similar
approach was used by Pineau des Forets & Roueff (2000) for the study of
chemical bistability. All the species are divided into 6 sensitivity groups
according to the value of the scatter in their model abundances computed with
varied rate constants. It is shown that the distribution of species within
these groups depends on the number of atoms in a molecule and on the adopted
physical conditions. The simple method is suggested which allows to single out
reactions that are most important for the evolution of a given species.Comment: 4 pages. To appear in the proceedings of the 4th Cologne-Bonn Zermatt
Symposiu
Insulating behavior in ultra-thin bismuth selenide field effect transistors
Ultrathin (~3 quintuple layer) field-effect transistors (FETs) of topological
insulator Bi2Se3 are prepared by mechanical exfoliation on 300nm SiO2/Si
susbtrates. Temperature- and gate-voltage dependent conductance measurements
show that ultrathin Bi2Se3 FETs are n-type, and have a clear OFF state at
negative gate voltage, with activated temperature-dependent conductance and
energy barriers up to 250 meV
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