434 research outputs found
On calculation of effective galvanomagnetic characteristics of inhomogeneous metals. Exact solution for the longitudinal effective conductivity of polycrystals of metals in high magnetic fields
In the framework of the perturbation theory an expression suitable for
calculation of the effective conductivity of 3-D inhomogeneous metals in
uniform magnetic field is derived. For polycrystals of metals with closed
Fermi surfaces in high magnetic fields the perturbation series defining the
longitudinal and the hall elements of the perturbation series can be summed
allowing us to obtain the exact expression for the leading terms of all these
elements of the effective conductivity tensor.Comment: 12 page
Duality and exact results for conductivity of 2D isotropic heterophase systems in magnetic field
Using a fact that the effective conductivity sigma_{e} of 2D random
heterophase systems in the orthogonal magnetic field is transformed under some
subgroup of the linear fractional group, connected with a group of linear
transformations of two conserved currents, the exact values for sigma_{e} of
isotropic heterophase systems are found. As known, for binary (N=2) systems a
determination of exact values of both conductivities (diagonal sigma_{ed} and
transverse Hall sigma_{et}) is possible only at equal phase concentrations and
arbitrary values of partial conductivities. For heterophase (N > 2) systems
this method gives exact values of effective conductivities, when their partial
conductivities belong to some hypersurfaces in the space of these partial
conductivities and the phase concentrations are pairwise equal. In all these
cases sigma_e does not depend on phase concentrations. The complete,
3-parametric, explicit transformation, connecting sigma_e in binary systems
with a magnetic field and without it, is constructedComment: 15 pages, 3 figures, Latex2
Conformal Invariance and Shape-Dependent Conductance of Graphene Samples
For a sample of an arbitrary shape, the dependence of its conductance on the
longitudinal and Hall conductivity is identical to that of a rectangle. We use
analytic results for a conducting rectangle, combined with the semicircle model
for transport coefficients, to study properties of the monolayer and bilayer
graphene. A conductance plateau centered at the neutrality point, predicted for
square geometry, is in agreement with recent experiments. For rectangular
geometry, the conductance exhibits maxima at the densities of compressible
quantum Hall states for wide samples, and minima for narrow samples. The
positions and relative sizes of these features are different in the monolayer
and bilayer cases, indicating that the conductance can be used as a tool for
sample diagnostic.Comment: 9 pages, 6 figure
Photon echoes of molecular photoassociation
Revivals of optical coherence of molecular photoassociation driven by two
ultrashort laser pulses are addressed in the Condon approach. Based on textbook
examples and numerical simulation of KrF excimer molecules, a prediction is
made about an existence of photon echo on free-bound transitions. Delayed rise
and fall of nonlinear polarization in the half-collisions are to be resulted
from the resonant quantum states interference whether it be in gas, liquid or
solid phases.Comment: 15 pages and 5 figures presented at ICONO '98'(Moscow, 1998):
Fundamental Aspects of Laser-Matter Interaction, New Nonlinear Optical
Materials and Physics of Low-Dimensional Structure
Wave of nonequilibrium ionization in a gas
Propagation model for plane ionization wave in uniform electric fiel
Strong-field dipole resonance. I. Limiting analytical cases
We investigate population dynamics in N-level systems driven beyond the
linear regime by a strong external field, which couples to the system through
an operator with nonzero diagonal elements. As concrete example we consider the
case of dipolar molecular systems. We identify limiting cases of the
Hamiltonian leading to wavefunctions that can be written in terms of ordinary
exponentials, and focus on the limits of slowly and rapidly varying fields of
arbitrary strength. For rapidly varying fields we prove for arbitrary that
the population dynamics is independent of the sign of the projection of the
field onto the dipole coupling. In the opposite limit of slowly varying fields
the population of the target level is optimized by a dipole resonance
condition. As a result population transfer is maximized for one sign of the
field and suppressed for the other one, so that a switch based on flopping the
field polarization can be devised. For significant sign dependence the
resonance linewidth with respect to the field strength is small. In the
intermediate regime of moderate field variation, the integral of lowest order
in the coupling can be rewritten as a sum of terms resembling the two limiting
cases, plus correction terms for N>2, so that a less pronounced sign-dependence
still exists.Comment: 34 pages, 1 figur
Magnetic screening in proximity effect Josephson-junction arrays
The modulation with magnetic field of the sheet inductance measured on
proximity effect Josephson-junction arrays (JJAs) is progressively vanishing on
lowering the temperature, leading to a low temperature field-independent
response. This behaviour is consistent with the decrease of the two-dimensional
penetration length below the lattice parameter. Low temperature data are
quantitatively compared with theoretical predictions based on the XY model in
absence of thermal fluctuations. The results show that the description of a JJA
within the XY model is incomplete and the system is put well beyond the weak
screening limit which is usually assumed in order to invoke the well known
frustrated XY model describing classical Josephson-junction arrays.Comment: 6 pages, 5 figure
Effective Drag Between Strongly Inhomogeneous Layers: Exact Results and Applications
We generalize Dykhne's calculation of the effective resistance of a 2D
two-component medium to the case of frictional drag between the two parallel
two-component layers. The resulting exact expression for the effective
transresistance, , is analyzed in the limits when the resistances
and transresistances of the constituting components are strongly different -
situation generic for the vicinity of the {\em classical} (percolative)
metal-insulator transition (MIT). On the basis of this analysis we conclude
that the evolution of across the MIT is determined by the type
of correlation between the components, constituting the 2D layers. Depending on
this correlation, in the case of two electron layers, changes
either monotonically or exhibits a sharp maximum. For electron-hole layers
is negative and exhibits a sharp minimum at the
MIT.Comment: 7 pages, 3 figure
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