754,249 research outputs found
Nonlinear conductance of nanowires - A signature of Luttinger liquid effects?
We analyze recent measurements of the room temperature current-voltage
characteristics of gold nanowires, whose zero current conductance is quantized
in units of . A faster than linear increase of current with voltage was
observed at low voltages beginning from V. We analyze the nonlinear
behavior in terms of a dynamic Coulomb blockade of conducting modes and show
that it may be explained as a Luttinger-liquid effect.Comment: 13 pages, latex with supplied stylefile, 3 figures in eps format,
submitted to Superlattices and Microstructure
Optical orientation of electron spins in GaAs quantum wells
We present a detailed experimental and theoretical analysis of the optical
orientation of electron spins in GaAs/AlAs quantum wells. Using time and
polarization resolved photoluminescence excitation spectroscopy, the initial
degree of electron spin polarization is measured as a function of excitation
energy for a sequence of quantum wells with well widths between 63 Ang and 198
Ang. The experimental results are compared with an accurate theory of excitonic
absorption taking fully into account electron-hole Coulomb correlations and
heavy-hole light-hole coupling. We find in wide quantum wells that the measured
initial degree of polarization of the luminescence follows closely the spin
polarization of the optically excited electrons calculated as a function of
energy. This implies that the orientation of the electron spins is essentially
preserved when the electrons relax from the optically excited high-energy
states to quasi-thermal equilibrium of their momenta. Due to initial spin
relaxation, the measured polarization in narrow quantum wells is reduced by a
constant factor that does not depend on the excitation energy.Comment: 12 pages, 9 figure
Bosonization solution of the Falicov-Kimball model
We use a novel approach to analyze the one dimensional spinless
Falicov-Kimball model. We derive a simple effective model for the occupation of
the localized orbitals which clearly reveals the origin of the known ordering.
Our study is extended to a quantum model with hybridization between the
localized and itinerant states; we find a crossover between the well-known
weak- and strong-coupling behaviour. The existence of electronic polarons at
intermediate coupling is confirmed. A phase diagram is presented and discussed
in detail.Comment: RevTex, 10 pages, 1 figur
The two types of Cherenkov gluons at LHC energies
Beside comparatively low energy Cherenkov gluons observed at RHIC, there
could be high energy gluons at LHC, related to the high energy region of
positive real part of the forward scattering amplitude. In both cases they give
rise to particles emitted along some cone. The characteristics of the cones
produced by these two types of gluons are different. Therefore different
experiments are needed to detect them. The cosmic ray event which initiated
this idea is described in detail.Comment: 6 pages, talk at IWCF2006, Hangzhou, Chin
Spin-torque resonance due to diffusive dynamics at a surface of topological insulator
We investigate spin-orbit torques on magnetization in an insulating
ferromagnetic (FM) layer that is brought into a close proximity to a
topological insulator (TI). In addition to the well-known field-like spin-orbit
torque, we identify an anisotropic anti-damping-like spin-orbit torque that
originates in a diffusive motion of conduction electrons. This diffusive torque
is vanishing in the limit of zero momentum (i. e. for spatially homogeneous
electric field or current), but may, nevertheless, have a strong effect on
spin-torque resonance at finite frequency provided external field is neither
parallel nor perpendicular to the TI surface. The required electric field
configuration can be created by a grated top gate.Comment: 10 page main text, 3 figure
Study of Beam Diagnostics with Trapped Modes in Third Harmonic Superconducting Cavities at FLASH
Off-axis beams passing through an accelerating cavity excite dipole modes
among other higher order modes (HOMs). These modes have linear dependence on
the transverse beam offset from the cavity axis. Therefore they can be used to
monitor the beam position within the cavity. The fifth dipole passband of the
third harmonic superconducting cavities at FLASH has modes trapped within each
cavity and do not propagate through the adjacent beam pipes, while most other
cavity modes do. This could enable the beam position measurement in individual
cavities. This paper investigates the possibility to use the fifth dipole band
for beam alignment in the third harmonic cavity module. Simulations and
measurements both with and without beam-excitations are presented. Various
analysis methods are used and compared. A good correlation of HOM signals to
the beam position is observed.Comment: 2nd International Particle Accelerator Conference (IPAC '11), San
Sebastian, Spain, Sep 4-9, 201
Band structure and magnetotransport of a two-dimensional electron gas in the presence of spin-orbit interaction
The band structure and magnetotransport of a two-dimensional electron gas
(2DEG), in the presence of the Rashba (RSOI) and Dresselhaus (DSOI) terms of
the spin-orbit interaction and of a perpendicular magnetic field, is
investigated. Exact and approximate analytical expressions for the band
structure are obtained and used to calculate the density of states (DOS) and
the longitudinal magnetoresitivity assuming a Gaussian type of level
broadening. The interplay between the Zeeman coupling and the two terms of the
SOI is discussed. If the strengths and , of the RSOI and DSOI,
respectively, are equal and the factor vanishes, the two spin states are
degenerate and a shifted Landau-level structure appears. With the increase of
the difference , a novel beating pattern of the DOS and of the
Shubnikov-de Haas (SdH) oscillations appears distinctly different from that
occurring when one of these strengths vanishes
- …