97 research outputs found
Carrier relaxation in Si/SiO quantum dots
Carrier relaxation due to both optical and nonradiative intraband transitions
in silicon quantum dots in SiO has been considered. Interaction of confined
holes with optical phonons has been studied. The Huang-Rhys factor is
calculated for such transitions. The probability of intraband transition of a
confined hole emitting several optical phonons is estimated.Comment: 8 pages, 2 figures, submitted as an extended abstract to the E-MRS
Spring Meeting 200
Specific Heat Discontinuity in Impure Two-Band Superconductors
The Ginzburg-Landau coefficients, and the jump of the specific heat are
calculated for a disordered two-band superconductor. We start with the analysis
of a more general case arbitrary anisotropy. While the specific heat
discontinuity at the critical temperature T_c decreases with increasing
disorder, its ratio to the normal state specific heat at T_c increases and
slowly converges to the isotropic value. For a strong disorder the deviation
from the isotropic value is proportional to the elastic electron scattering
time. In the case of a two-band superconductor we apply a simplified model of
the interaction independent on momentum within a band. In the framework of this
model all thermodynamic values can be found explicitly at any value of the
scattering rate. This solution explains the sample dependence of the specific
heat discontinuity in MgB_2 and the influence of the disorder on the critical
temperature.Comment: New results relate to two-band superconductors, 9 pages, 2 figure
Is there any future of optical discs?
Considered in this paper are causes for cutting compact discs out of
information technology market. It has been shown a search of new technological
solutions for efficient use of CDs in archive data storage
Optical recording of information pits in thin layers of chalcogenide semiconductors
The paper is devoted to the theoretical consideration of the question how to record pits with the necessary height profile in photosensitive materials by varying their heat conductivity, photosensitivity, optical absorption, as well as the recording gaussian beam intensity,
radius and exposure time. A rather simple analytical expression for the height profile of pits has been derived. It has been shown that this profile depending on photosensitive material parameters and recording beam characteristics could be almost rectangular, flat with rounding edges, spherical or parabolic. The proposed model describes adequately the height profile of pits recorded in thin layer chalcogenide semiconductors by a gaussian laser beam
Coupling between planes and chains in YBa2Cu3O7 : a possible solution for the order parameter controversy
We propose to explain the contradictory experimental evidence about the
symmetry of the order parameter in by taking into account
the coupling between planes and chains. This leads to an anticrossing of the
plane and chain band. We include an attractive pairing interaction within the
planes and a repulsive one between planes and chains, leading to opposite signs
for the order parameter on planes and chains, and to nodes of the gap because
of the anticrossing. Our model blends s-wave and d-wave features, and provides
a natural explanation for all the contradictory experimentsComment: 13 pages, revtex, 2 uucoded figure
Effect of magnetic and non-magnetic impurities on highly anisotropic superconductivity
We generalize Abrikosov-Gor'kov solution of the problem of weakly coupled
superconductor with impurities on the case of a multiband superconductor with
arbitrary interband order parameter anisotropy, including interband sign
reversal of the order parameter. The solution is given in terms of the
effective (renormalized) coupling matrix and describes not only
suppression but also renormalization of the superconducting gap basically at
all temperatures. In many limiting cases we find analytical solutions for the
critical temperature suppression. We illustrate our results by numerical
calculations for two-band model systems.Comment: 18 pages (12pt) RevTeX, 4 postscript figure
Landau quantization of two-dimensional heavy holes, energy spectrum of magnetoexcitons and Auger-recombination lines
The Landau quantization of the two-dimensional (2D) heavy holes, its influence on the energy spectrum of 2D magnetoexcitons, as well as their optical orientation are studied. The Hamiltonian of the heavy holes is written in two-band model taking into account the Rashba spin-orbit coupling (RSOC) with two spin projections, but with nonparabolic dispersion law and third-order chirality terms. The most Landau levels, except three with m=0,1,2, are characterized by two quantum numbers m-3 and m for m≥3 for two spin projections correspondingly. The difference between them is determined by the third-order chirality. Four lowest Landau levels (LLLs) for heavy holes were combined with two LLLs for conduction electron, which were taken the same as they were deduced by Rashba in his theory of spin-orbit coupling (SOC) based on the initial parabolic dispersion law and first-order chirality terms. As a result of these combinations eight 2D magnetoexciton states were formed. Their energy spectrum and the selection rules for the quantum transitions from the ground state of the crystal to exciton states were determined. On this base such optical orientation effects as spin polarization and magnetoexciton alignment are discussed. The continuous transformation of the shake-up (SU) into the shake-down (SD) recombination lines is explained on the base of nonmonotonous dependence of the heavy hole Landau quantization levels as a function of applied magnetic field. © 2013 Elsevier B.V. All rights reserved
Sign reversal of the order parameter in s-wave superconductors
We show that in a superconductor where two or more bands cross the Fermi
level it is possible, in the framework of the conventional (s-wave) BCS theory,
that the sign of the superconducting gap is different on the different sheets
of the Fermi surface. At least one of two conditions has to be satisfied: (1)
The interband pairing interaction is weaker than the Coulomb pseudopotential,
while the intraband one is stronger, or (2) there is strong interband
scattering by magnetic impurities. In the case of YBa% CuO we shall
argue that the first condition is possibly satisfied, and the second one very
likely satisfied. In many aspects such a sign-reversal wave superconductor
is similar to a d-wave superconductor, and thus demands revising recent
experiments aimed to distinguish between the and wave
superconductivity in this compound.Comment: RevTex; Physica C, in pres
Penetration depth anisotropy in two-band superconductors
The anisotropy of the London penetration depth is evaluated for two-band
superconductors with arbitrary inter- and intra-band scattering times. If one
of the bands is clean and the other is dirty in the absence of inter-band
scattering, the anisotropy is dominated by the Fermi surface of the clean band
and is weakly temperature dependent. The inter-band scattering also suppress
the temperature dependence of the anisotropy
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