12,945 research outputs found
Magnetoresistance, noise properties and the Koshino-Taylor effect in the quasi-1D oxide KRu_4O_8
The low temperature electronic and galvanomagnetic transport properties of
the low dimensional oxide KRu_4O_8 are experimentally considered. A quadratic
temperature variation of the resistivity is observed to be proportional to the
residual resistivity. It shows the role of inelastic electron scattering
against impurities, i.e. a large Koshino-Taylor effect, rather than a
consequence of strong electronic correlations. In the same temperature range,
the Kohler rule is not fulfilled. The resistance noise increases also sharply,
possibly due to a strong coupling of carriers with lattice fluctuations in this
low dimensional compound.Comment: accepted for publication in Europhysics Lette
A discrete time relativistic Toda lattice
Four integrable symplectic maps approximating two Hamiltonian flows from the
relativistic Toda hierarchy are introduced. They are demostrated to belong to
the same hierarchy and to examplify the general scheme for symplectic maps on
groups equiped with quadratic Poisson brackets. The initial value problem for
the difference equations is solved in terms of a factorization problem in a
group. Interpolating Hamiltonian flows are found for all the maps.Comment: 32 pages, LaTe
Poisson structures for reduced non-holonomic systems
Borisov, Mamaev and Kilin have recently found certain Poisson structures with
respect to which the reduced and rescaled systems of certain non-holonomic
problems, involving rolling bodies without slipping, become Hamiltonian, the
Hamiltonian function being the reduced energy. We study further the algebraic
origin of these Poisson structures, showing that they are of rank two and
therefore the mentioned rescaling is not necessary. We show that they are
determined, up to a non-vanishing factor function, by the existence of a system
of first-order differential equations providing two integrals of motion. We
generalize the form of that Poisson structures and extend their domain of
definition. We apply the theory to the rolling disk, the Routh's sphere, the
ball rolling on a surface of revolution, and its special case of a ball rolling
inside a cylinder.Comment: 22 page
Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-2D organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br: quest for intrinsic scattering contributions
Resistivity measurements have been performed on a low (LR)- and high
(HR)-resistance variant of the kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br superconductor.
While the HR sample was synthesized following the standard procedure, the LR
crystal is a result of a somewhat modified synthesis route. According to their
residual resistivities and residual resistivity ratios, the LR crystal is of
distinctly superior quality. He-gas pressure was used to study the effect of
hydrostatic pressure on the different transport regimes for both variants. The
main results of these comparative investigations are (i) a significant part of
the inelastic-scattering contribution, which causes the anomalous rho(T)
maximum in standard HR crystals around 90 K, is sample dependent, i.e.
extrinsic in nature, (ii) the abrupt change in rho(T) at T* approx. 40 K from a
strongly temperature-dependent behavior at T > T* to an only weakly T-dependent
rho(T) at T < T* is unaffected by this scattering contribution and thus marks
an independent property, most likely a second-order phase transition, (iii)
both variants reveal a rho(T) proportional to AT^2 dependence at low
temperatures, i.e. for T_c < T < T_0, although with strongly sample-dependent
coefficients A and upper bounds for the T^2 behavior measured by T_0. The
latter result is inconsistent with the T^2 dependence originating from coherent
Fermi-liquid excitations.Comment: 8 pages, 6 figure
Lowest weight representations of super Schrodinger algebras in low dimensional spacetime
We investigate the lowest weight representations of the super Schrodinger
algebras introduced by Duval and Horvathy. This is done by the same procedure
as the semisimple Lie algebras. Namely, all singular vectors within the Verma
modules are constructed explicitly then irreducibility of the associated
quotient modules is studied again by the use of singular vectors. We present
the classification of irreducible Verma modules for the super Schrodinger
algebras in (1+1) and (2+1) dimensional spacetime with N = 1, 2 extensions.Comment: 10pages, talk given at GROUP28 conference New Castle 26-30th July
2010, reference adde
Van der Waals interaction between microparticle and uniaxial crystal with application to hydrogen atoms and multiwall carbon nanotubes
The Lifshitz theory of the van der Waals force is extended for the case of an
atom (molecule) interacting with a plane surface of an uniaxial crystal or with
a long solid cylinder or cylindrical shell made of isotropic material or
uniaxial crystal. For a microparticle near a semispace or flat plate made of an
uniaxial crystal the exact expressions for the free energy of the van der Waals
and Casimir-Polder interaction are presented. An approximate expression for the
free energy of microparticle- cylinder interaction is obtained which becomes
precise for microparticle-cylinder separations much smaller than cylinder
radius. The obtained expressions are used to investigate the van der Waals
interaction between hydrogen atoms (molecules) and graphite plates or multiwall
carbon nanotubes. To accomplish this the behavior of graphite dielectric
permittivities along the imaginary frequency axis is found using the optical
data for the complex refractive index of graphite for the ordinary and
extraordinary rays. It is shown that the position of hydrogen atoms inside
multiwall carbon nanotubes is energetically preferable compared with outside.Comment: 23 pages, 8 figures, 2 tables. Minor corrections are made and new
references added. Accepted for publication in Phys. Rev.
Theoretical study of neutrino-induced coherent pion production off nuclei at T2K and MiniBooNE energies
We have developed a model for neutrino-induced coherent pion production off
nuclei in the energy regime of interest for present and forthcoming neutrino
oscillation experiments. It is based on a microscopic model for pion production
off the nucleon that, besides the dominant Delta pole contribution, takes into
account the effect of background terms required by chiral symmetry. Moreover,
the model uses a reduced nucleon-to-Delta resonance axial coupling, which leads
to coherent pion production cross sections around a factor two smaller than
most of the previous theoretical estimates. In the coherent production, the
main nuclear effects, namely medium corrections on the Delta propagator and the
final pion distortion, are included. We have improved on previous similar
models by taking into account the nucleon motion and employing a more
sophisticated optical potential. As found in previous calculations the
modification of the Delta self-energy inside the nuclear medium strongly
reduces the cross section, while the final pion distortion mainly shifts the
peak position to lower pion energies. The angular distribution profiles are not
much affected by nuclear effects. Nucleon motion increases the cross section by
15% at neutrino energies of 650 MeV, while Coulomb effects on charged pions are
estimated to be small. Finally, we discuss at length the deficiencies of the
Rein-Sehgal pion coherent production model for neutrino energies below 2 GeV,
and in particular for the MiniBooNE and T2K experiments. We also predict flux
averaged cross sections for these two latter experiments and K2K.Comment: 19 latex pages, 10 figures, 2 tables. Minor changes. Version accepted
for publication in Physical Review
A Factorization Law for Entanglement Decay
We present a simple and general factorization law for quantum systems shared
by two parties, which describes the time evolution of entanglement upon passage
of either component through an arbitrary noisy channel. The robustness of
entanglement-based quantum information processing protocols is thus easily and
fully characterized by a single quantity.Comment: 4 pages, 5 figure
Quasiparticle Bound States and Low-Temperature Peaks of the Conductance of NIS Junctions in d-Wave Superconductors
Quasiparticle states bound to the boundary of anisotropically paired
superconductors, their contributions to the density of states and to the
conductance of NIS junctions are studied both analytically and numerically. For
smooth surfaces and real order parameter we find some general results for the
bound state energies. In particular, we show that under fairly general
conditions quasiparticle states with nonzero energies exist for momentum
directions within a narrow region around the surface normal. The energy
dispersion of the bound states always has an extremum for the direction along
the normal. Along with the zero-bias anomaly due to midgap states, we find, for
quasi two-dimensional materials, additional low-temperature peaks in the
conductance of NIS junctions for voltages determined by the extrema of the
bound state energies. The influence of interface roughness on the conductance
is investigated within the framework of Ovchinnikov's model. We show that
nonzero-bias peaks at low temperatures may give information on the order
parameter in the bulk, even though it is suppressed at the surface.Comment: 14 pages, PostScrip
Cooling of Neutron Stars: Two Types of Triplet Neutron Pairing
We consider cooling of neutron stars (NSs) with superfluid cores composed of
neutrons, protons, and electrons (assuming singlet-state pairing of protons,
and triplet-state pairing of neutrons). We mainly focus on (nonstandard)
triplet-state pairing of neutrons with the projection of the total
angular momentum of Cooper pairs onto quantization axis. The specific feature
of this pairing is that it leads to a power-law (nonexponential) reduction of
the emissivity of the main neutrino processes by neutron superfluidity. For a
wide range of neutron critical temperatures , the cooling of NSs with
the superfluidity is either the same as the cooling with the superfluidity, considered in the majority of papers, or much faster. The
cooling of NSs with density dependent critical temperatures and
can be imitated by the cooling of the NSs with some effective
critical temperatures and constant over NS cores. The
hypothesis of strong neutron superfluidity with is inconsistent
with current observations of thermal emission from NSs, but the hypothesis of
weak neutron superfluidity of any type does not contradict to observations.Comment: 10 pages, 6 figure
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