65 research outputs found
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
Interatomic potentials for the vibrational properties of III-V semiconductor nanostructures
We derive interatomic potentials for zinc blende InAs, InP, GaAs and GaP
semiconductors with possible applications in the realm of nanostructures. The
potentials include bond stretching interaction between the nearest and
next-nearest neighbors, a three body term and a long-range Coulomb interaction.
The optimized potential parameters are obtained by (i) fitting to bulk phonon
dispersions and elastic properties and (ii) constraining the parameter space to
deliver well behaved potentials for the structural relaxation and vibrational
properties of nanostructure clusters. The targets are thereby calculated by
density functional theory for clusters of up to 633 atoms. We illustrate the
new capability by the calculation Kleinman and Gr\"uneisen parameters and of
the vibrational properties of nanostructures with 3 to 5.5 nm diameter.Comment: 22 pages, 5 figures; Phys. Rev. B 201
Carrier relaxation mechanisms in self-assembled (In,Ga)As/GaAs quantum dots: Efficient P -> S Auger relaxation of electrons
We calculate the P-shell--to-S-shell decay lifetime \tau(P->S) of electrons
in lens-shaped self-assembled (In,Ga)As/GaAs dots due to Auger electron-hole
scattering within an atomistic pseudopotential-based approach. We find that
this relaxation mechanism leads to fast decay of \tau(P->S)~1-7 ps for dots of
different sizes. Our calculated Auger-type P-shell--to-S-shell decay lifetimes
\tau(P->S) compare well to data in (In,Ga)As/GaAs dots, showing that as long as
holes are present there is no need for an alternative polaron mechanism.Comment: Version published in Phys. Rev.
Response of the topological surface state to surface disorder in TlBiSe
Through a combination of experimental techniques we show that the topmost
layer of the topo- logical insulator TlBiSe as prepared by cleavage is
formed by irregularly shaped Tl islands at cryogenic temperatures and by mobile
Tl atoms at room temperature. No trivial surface states are observed in
photoemission at low temperatures, which suggests that these islands can not be
re- garded as a clear surface termination. The topological surface state is,
however, clearly resolved in photoemission experiments. This is interpreted as
a direct evidence of its topological self-protection and shows the robust
nature of the Dirac cone like surface state. Our results can also help explain
the apparent mass acquisition in S-doped TlBiSe.Comment: 16 pages, 5 figure
Unconventional transformation of spin Dirac phase across a topological quantum phase transition
The topology of a topological material can be encoded in its surface states.
These surface states can only be removed by a bulk topological quantum phase
transition into a trivial phase. Here we use photoemission spectroscopy to
image the formation of protected surface states in a topological insulator as
we chemically tune the system through a topological transition. Surprisingly,
we discover an exotic spin-momentum locked, gapped surface state in the trivial
phase that shares many important properties with the actual topological surface
state in anticipation of the change of topology. Using a spin-resolved
measurement, we show that apart from a surface band-gap these states develop
spin textures similar to the topological surface states well-before the
transition. Our results offer a general paradigm for understanding how surface
states in topological phases arise and are suggestive for future realizing Weyl
arcs, condensed matter supersymmetry and other fascinating phenomena in the
vicinity of topological quantum criticality.Comment: 20 pages, 5 Figures, Related papers at
http://physics.princeton.edu/zahidhasangroup/index.html, Accepted for
publication in Nature Commun.(2015
ISO continuum observations of quasars at z=1-4 I.Spectral energy distributions of quasars from the UV to far-infrared
Eight luminous quasars with at z = 1.4 - 3.7 have been
observed in the mid- and far-infrared using ISO. All the quasars have been
detected in the mid-infrared bands of ISOCAM, while no far-infrared detections
have been made with ISOPHOT. Supplementing ISO observations with photometry in
the optical and near-infrared made from the ground mostly within 17 months
after the ISO observations, SEDs (Spectral Energy Distributions) from the UV to
far-infrared have been obtained. SEDs (Spectral Energy Distributions) from the
UV to far-infrared have been obtained while supplementing ISO observations with
photometry in the optical and near-infrared made from the ground within 17
months. The SEDs are compared with the MED (Mean spectral Energy Distributions)
of low-redshift quasars with . It is shown that our
far-infrared observations were limited by confusion noise due to crowded
sources.Comment: 9 pages, 3 figures: accepted for publication in Astronomy and
Astrophysic
Response of Duplex Cr(N)/S and Cr(C)/S Coatings on 316L Stainless Steel to Tribocorrosion in 0.89% NaCl Solution Under Plastic Contact Conditions
This is the peer reviewed version of the following article: Sun Y, Dearnley PA, Mallia B. 2016. Response of duplex Cr(N)/S and Cr(C)/S coatings on 316L stainless steel to tribocorrosion in 0.89% NaCl solution under plastic contact conditions. J Biomed Mater Res Part B 2016:00B:000–000, which has been published in final form at [10.1002/jbm.b.33690. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Two duplex coatings, Cr(N)/S and Cr(C)/S, were deposited on 316L stainless steel by magnetron sputtering. The effectiveness of these duplex coatings in improving the tribocorrosion behaviour of medical alloys under elastic contact conditions has been demonstrated in a recent publication. The present work focused on the response of these duplex coatings to tribocorrosion under plastic contact conditions. Tribocorrosion tests were conducted in 0.89 % NaCl solution at 37oC at an initial contact pressure of 740 MPa and under unidirectional sliding conditions for sliding duration up to 24 h. The results showed that during sliding in the corrosive solution, the duplex coatings were plastically deformed into the substrate to a depth about 1 m. The Cr(C)/S duplex coating had sufficient ductility to accommodate the deformation without cracking, such that it was worn through gradually, leading to the gradual increase in open circuit potential (OCP) and coefficient of friction (COF). On the other hand, the Cr(N)/S duplex coating suffered from cracking at all tested potentials, leading to coating blistering after prolonged sliding at OCP and stable pit formation in the substrate beneath the coating at applied anodic potentials
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