53 research outputs found
Ginzburg-Landau theory of vortices in a multi-gap superconductor
The Ginzburg-Landau functional for a two-gap superconductor is derived within
the weak-coupling BCS model. The two-gap Ginzburg-Landau theory is, then,
applied to investigate various magnetic properties of MgB2 including an upturn
temperature dependence of the transverse upper critical field and a core
structure of an isolated vortex. Orientation of vortex lattice relative to
crystallographic axes is studied for magnetic fields parallel to the c-axis. A
peculiar 30-degree rotation of the vortex lattice with increasing strength of
an applied field observed by neutron scattering is attributed to the multi-gap
nature of superconductivity in MgB2.Comment: 11 page
Thermoelectric power of nondegenerate Kane semiconductors under the conditions of mutual electron-phonon drag in a high electric field
The thermoelectric power of nondegenerate Kane semiconductors with due regard
for the electron and phonon heating, and their thermal and mutual drags is
investigated. The electron spectrum is taken in the Kane two-band form. It is
shown that the nonparabolicity of electron spectrum significantly influences
the magnitude of the thermoelectric power and leads to a change of its sign and
dependence on the heating electric field. The field dependence of the
thermoelectric power is determined analytically under various drag conditions.Comment: 25 pages, RevTex formatted, 3 table
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
Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors
Quasiclassic Uzadel equations for two-band superconductors in the dirty limit
with the account of both intraband and interband scattering by nonmagnetic
impurities are derived for any anisotropic Fermi surface. From these equations
the Ginzburg-Landau equations, and the critical temperature are obtained.
An equation for the upper critical field, which determines both the temperature
dependence of and the orientational dependence of
as a function of the angle between and the c-axis is
obtained. It is shown that the shape of the curve essentially
depends on the ratio of the intraband electron diffusivities and ,
and can be very different from the standard one-gap dirty limit theory. In
particular, the value can considerably exceed ,
which can have important consequences for applications of . A scaling
relation is proposed which enables one to obtain the angular dependence of
from the equation for at . It is shown
that, depending on the relation between and , the ratio of the upper
critical field for and can both increase and decrease as the temperature decreases. Implications
of the obtained results for are discussed
Upper critical field in dirty two-band superconductors: breakdown of the anisotropic Ginzburg-Landau theory
We investigate the upper critical field in a dirty two-band superconductor
within quasiclassical Usadel equations. The regime of very high anisotropy in
the quasi-2D band, relevant for MgB, is considered. We show that strong
disparities in pairing interactions and diffusion constant anisotropies for two
bands influence the in-plane in a different way at high and low
temperatures. This causes temperature-dependent anisotropy, in
accordance with recent experimental data in MgB. The three-dimensional
band most strongly influences the in-plane near , in the
Ginzburg-Landau (GL) region. However, due to a very large difference between
the c-axis coherence lengths in the two bands, the GL theory is applicable only
in an extremely narrow temperature range near . The angular dependence of
deviates from a simple effective-mass law even near .Comment: 12 pages, 5 figures, submitted to Phys.Rev.
The first dozen years of the history of ITEP Theoretical Physics Laboratory
The theoretical investigations at ITEP in the years 1945-1958 are reviewed.
There are exposed the most important theoretical results, obtained in the
following branches of physics: 1) the theory of nuclear reactors on thermal
neutrons; 2) the hydrogen bomb project ("Tube" in USSR and "Classical Super" in
USA); 3) radiation theory; ~4) low temperature physics; 5) quantum
electrodynamics and quantum field theories; 6) parity violation in weak
interactions, the theory of -decay and other weak processes; 7) strong
interaction and nuclear physics. To the review are added the English
translations of few papers, originally published in Russian, but unknown (or
almost unknown) to Western readers.Comment: 55 pages, 5 fig
The Fulde–Ferrell–Larkin–Ovchinnikov State in Pnictides
Fe-based superconductors (FeSC) exhibit all the properties of systems that
allow the formation of a superconducting phase with oscillating order
parameter, called the Fulde--Ferrell--Larkin--Ovchinnikov (FFLO) phase. By the
analysis of the Cooper pair susceptibility in two-band FeSC, such systems are
shown to support the existence of a FFLO phase, regardless of the exhibited
order parameter symmetry. We also show the state with nonzero Cooper pair
momentum, in superconducting FeSC with
symmetry, to be the ground state of the system in a certain parameter range.Comment: 8 pages, 4 figures Journal of Low Temperature Physics, (2013
Measurement of the beam-helicity asymmetry in photoproduction of π0η pairs on carbon, aluminum, and lead
The beam-helicity asymmetry was measured, for the first time, in photoproduction of
π0η pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for π0η pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the D33 partial wave with the ηΔ(1232) intermediate state
- …