6,690 research outputs found
Comment on "Is the nonlinear Meissner effect unobservable?"
In a recent Letter (Phys. Rev. Lett. 81, p.5640 (1998), cond-mat/9808249 v3),
it was suggested that nonlocal effects may prevent observation of the nonlinear
Meissner effect in YBCO. We argue that this claim is incorrect with regards to
measurements of the nonlinear transverse magnetic moment, and that the most
likely reason for a null result lies elsewhere.Comment: 1 pag
Discovery of a Wide Substellar Companion to a Nearby Low-Mass Star
We report the discovery of a wide (135+/-25 AU), unusually blue L5 companion
2MASS J17114559+4028578 to the nearby M4.5 dwarf G 203-50 as a result of a
targeted search for common proper motion pairs in the Sloan Digital Sky Survey
and the Two Micron All Sky Survey. Adaptive Optics imaging with Subaru
indicates that neither component is a nearly equal mass binary with separation
> 0.18", and places limits on the existence of additional faint companions. An
examination of TiO and CaH features in the primary's spectrum is consistent
with solar metallicity and provides no evidence that G 203-50 is metal poor. We
estimate an age for the primary of 1-5 Gyr based on activity. Assuming
coevality of the companion, its age, gravity and metallicity can be constrained
from properties of the primary, making it a suitable benchmark object for the
calibration of evolutionary models and for determining the atmospheric
properties of peculiar blue L dwarfs. The low total mass (M_tot=0.21+/-0.03
M_sun), intermediate mass ratio (q=0.45+/-0.14), and wide separation of this
system demonstrate that the star formation process is capable of forming wide,
weakly bound binary systems with low mass and BD components. Based on the
sensitivity of our search we find that no more than 2.2% of early-to-mid M
dwarfs (9.0 0.06 M_sun.Comment: 24 pages, 5 figures, accepted for publication in Ap
Quantum motion of a neutron in a wave-guide in the gravitational field
We study theoretically the quantum motion of a neutron in a horizontal
wave-guide in the gravitational field of the Earth. The wave-guide in question
is equipped with a mirror below and a rough absorber above. We show that such a
system acts as a quantum filter, i.e. it effectively absorbs quantum states
with sufficiently high transversal energy but transmits low-energy states. The
states transmitted are mainly determined by the potential well formed by the
gravitational field of the Earth and the mirror. The formalism developed for
quantum motion in an absorbing wave-guide is applied to the description of the
recent experiment on the observation of the quantum states of neutrons in the
Earth's gravitational field
Effect of Fibonacci Modulation On Superconductivity
We have studied finite-sized single band models with short range pairing
interactions between electrons in presence of diagonal Fibonacci modulation in
one dimension. Two models, namely the attractive Hubbard model and the
Penson-Kolb model, have been investigated at half-filling at zero temperature
by solving the Bogoliubov-de Gennes equations in real space within a mean field
approximation. The competition between ``disorder'' and the pairing interaction
leads to a suppression of superconductivity (of usual pairs with zero
centre-of-mass momenta) in the strong-coupling limit while an enhancement of
the pairing correlation is observed in the weak-coupling regime for both the
models. However, the dissimilarity of the pairing mechanisms in these two
models brings about notable difference in the results. The extent to which the
bond ordered wave and the -paired (of pairs with centre-of-mass momenta =
) phases of the Penson-Kolb model are affected by the disorder has also
been studied in the present calculation. Some finite size effects are also
identified.Comment: 14 pages, 13 figure
Lifetime of metastable states in resonant tunneling structures
We investigate the transport of electrons through a double-barrier
resonant-tunneling structure in the regime where the current-voltage
characteristics exhibit bistability. In this regime one of the states is
metastable, and the system eventually switches from it to the stable state. We
show that the mean switching time grows exponentially as the voltage across the
device is tuned from the its boundary value into the bistable region. In
samples of small area we find that the logarithm of the lifetime is
proportional to the voltage (measured from its boundary value) to the 3/2
power, while in larger samples the logarithm of the lifetime is linearly
proportional to the voltage.Comment: REVTeX 4, 5 pages, 3 EPS-figure
Effects of resonant tunneling in electromagnetic wave propagation through a polariton gap
We consider tunneling of electromagnetic waves through a polariton band gap
of a 1-D chain of atoms. We analytically show that a defect embedded in the
structure gives rise to the resonance transmission at the frequency of a local
polariton state associated with the defect. Numerical Monte-Carlo simulations
are used to examine properties of the electromagnetic band arising inside the
polariton gap due to finite concentration of defects.Comment: 12 pages, 6 figures, RevTe
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