59,904 research outputs found
Probing the plateau-insulator quantum phase transition in the quantum Hall regime
We report quantum Hall experiments on the plateau-insulator transition in a
low mobility In_{.53} Ga_{.47} As/InP heterostructure. The data for the
longitudinal resistance \rho_{xx} follow an exponential law and we extract a
critical exponent \kappa= .55 \pm .05 which is slightly different from the
established value \kappa = .42 \pm .04 for the plateau transitions. Upon
correction for inhomogeneity effects, which cause the critical conductance
\sigma_{xx}^* to depend marginally on temperature, our data indicate that the
plateau-plateau and plateau- insulator transitions are in the same universality
class.Comment: 4 pages, 4 figures (.eps
Suppression of low-energy Andreev states by a supercurrent in YBa_2Cu_3O_7-delta
We report a coherence-length scale phenomenon related to how the high-Tc
order parameter (OP) evolves under a directly-applied supercurrent. Scanning
tunneling spectroscopy was performed on current-carrying YBa_2Cu_3O_7-delta
thin-film strips at 4.2K. At current levels well below the theoretical
depairing limit, the low-energy Andreev states are suppressed by the
supercurrent, while the gap-like structures remain unchanged. We rule out the
likelihood of various extrinsic effects, and propose instead a model based on
phase fluctuations in the d-wave BTK formalism to explain the suppression. Our
results suggest that a supercurrent could weaken the local phase coherence
while preserving the pairing amplitude. Other possible scenarios which may
cause the observed phenomenon are also discussed.Comment: 6 pages, 4 figures, to appear in Physical Review
Quantum interference in deformed carbon nanotube waveguides
Quantum interference (QI) in two types of deformed carbon nanotubes (CNTs),
i.e., axially stretched and AFM tip-deformed CNTs, has been investigated by the
pi-electron only and four-orbital tight-binding (TB) method. It is found that
the rapid conductance oscillation (RCO) period is very sensitive to the applied
strains, and decreases in an inverse proportion to the deformation degree,
which could be used as a powerful experimental tool to detect precisely the
deformation degree of the deformed CNTs. Also, the sigma-pi coupling effect is
found to be negligible under axially stretched strain, while it works on the
transport properties of the tip-deformed CNTs.Comment: 14 pages and 5 figure
Effects of topological edge states on the thermoelectric properties of Bi nanoribbons
Using first-principles calculations combined with Boltzmann transport theory,
we investigate the effects of topological edge states on the thermoelectric
properties of Bi nanoribbons. It is found that there is a competition between
the edge and bulk contributions to the Seebeck coefficients. However, the
electronic transport of the system is dominated by the edge states because of
its much larger electrical conductivity. As a consequence, a room temperature
value exceeding 3.0 could be achieved for both p- and n-type systems when the
relaxation time ratio between the edge and the bulk states is tuned to be 1000.
Our theoretical study suggests that the utilization of topological edge states
might be a promising approach to cross the threshold of the industrial
application of thermoelectricity
A dynamical approximation for stochastic partial differential equations
Random invariant manifolds often provide geometric structures for
understanding stochastic dynamics. In this paper, a dynamical approximation
estimate is derived for a class of stochastic partial differential equations,
by showing that the random invariant manifold is almost surely asymptotically
complete. The asymptotic dynamical behavior is thus described by a stochastic
ordinary differential system on the random invariant manifold, under suitable
conditions. As an application, stationary states (invariant measures) is
considered for one example of stochastic partial differential equations.Comment: 28 pages, no figure
Cosmological Models and Latest Observational Data
In this note, we consider the observational constraints on some cosmological
models by using the 307 Union type Ia supernovae (SNIa), the 32 calibrated
Gamma-Ray Bursts (GRBs) at , the updated shift parameter from WMAP
5-year data (WMAP5), and the distance parameter of the measurement of the
baryon acoustic oscillation (BAO) peak in the distribution of SDSS luminous red
galaxies with the updated scalar spectral index from WMAP5. The tighter
constraints obtained here update the ones obtained previously in the
literature.Comment: 10 pages, 5 figures, 1 table, revtex4; v2: discussions added,
accepted by Eur. Phys. J. C; v3: published versio
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