145 research outputs found
Scattering problems and boundary conditions for 2D electron gas and graphene
Structure and coordinate dependence of the reflected wave, as well as
boundary conditions for quasi-particles of graphene and the two dimensional
electron gas in sheets with abrupt lattice edges are obtained and analyzed by
the Green's function technique. In particular, the reflection wave function
contains terms inversely proportional to the distance to the graphene lattice
edge. The Dirac equation and the momentum dependence of the wave functions of
the quasi-particles near the conical points are also found by the perturbation
theory with degeneracy in terms of the Bloch functions taken at the degeneracy
points. The developed approach allows to formulated the validity criteria for
the Dirac equation in a rather simple way.Comment: 7 pages, 2 figure
Enhancement of magnetic ordering by the stress fields of grain boundaries in ferromagnets
In the paper we predict a distinctive change of magnetic properties and
considerable increase of the Curie temperature caused by the strain fields of
grain boundaries in ferromagnetic films. It is shown that a sheet of
spontaneous magnetization may arise along a grain boundary at temperatures
greater than the bulk Curie temperature. The temperature dependence and space
distribution of magnetization in a ferromagnetic film with grain boundaries are
calculated. We found that grain boundaries can produce long-range
strain fields that results in the width of the magnetic sheet along the
boundary of the order of at temperatures grater than the
bulk Curie temperature by about K.Comment: 5 pages, 3 Figures include
Giant oscillations of the current in a dirty 2D electron system flowing perpendicular to a lateral barrier under magnetic field
The charge transport in a dirty 2-dimensional electron system biased in the
presence of a lateral potential barrier under magnetic field is theoretically
studied. The quantum tunneling across the barrier provides the quantum
interference of the edge states localized on its both sides that results in
giant oscillations of the charge current flowing perpendicular to the lateral
junction. Our theoretical analysis is in a good agreement with the experimental
observations presented in Ref.8. In particular, positions of the conductance
maxima coincide with the Landau levels while the conductance itself is
essentially suppressed even at the energies at which the resonant tunneling
occurs and hence these puzzling observations can be resolved without taking
into account the electron-electron interaction.Comment: 6 pages, 4 figure
Sub-Wavelength Terahertz Spin-Flip Laser Based on a Magnetic Point-Contact Array
We present a novel design for a single-mode, truly sub-wavelength THz disk
laser based on a nano-composite gain medium comprising an array of
metal/ferromagnetic point contacts embedded in a thin dielectric layer.
Stimulated emission of light occurs in the point contacts as a result of
spin-flip relaxation of spin-polarized electrons that are injected from the
ferromagnetic side of the contacts. Ultra-high electrical current densities in
the contacts and a dielectric material with a large refractive index, neither
condition being achievable in conventional semiconductor media, allows the
thresholds of lasing to be overcome for the lowest-order modes of the disk,
hence making single-mode operation possible.Comment: 9 pages,4 figure
Peierls-type structural phase transition in a crystal induced by magnetic breakdown
We predict a new type of phase transition in a quasi-two dimensional system
of electrons at high magnetic fields, namely the stabilization of a density
wave which transforms a two dimensional open Fermi surface into a periodic
chain of large pockets with small distances between them. The quantum tunneling
of electrons between the neighboring closed orbits enveloping these pockets
transforms the electron spectrum into a set of extremely narrow energy bands
and gaps which decreases the total electron energy, thus leading to a magnetic
breakdown induced density wave (MBIDW) ground state. We show that this DW
instability has some qualitatively different properties in comparison to
analogous DW instabilities of Peierls type. E. g. the critical temperature of
the MBIDW phase transition arises and disappears in a peculiar way with a
change of the inverse magnetic field
Excess Resistance Effect in a Normal Metal Contacting a Superconductor
In relatively pure normal samples contacting a superconductor we consider the
excess resistance effect (that is a decrease of the total electrical resistance
of the sample after transition of the superconducting part into the normal
state) and determine conditions under which the effect arises.Comment: 3 pages, 2 postscript figures all in uuencoded forma
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