589 research outputs found
Density of states in SF bilayers with arbitrary strength of magnetic scattering
We developed the self-consistent method for the calculation of the density of
states in the SF bilayers. It based on the quasi-classical Usadel
equations and takes into account the suppression of superconductivity in the S
layer due to the proximity effect with the F metal, as well as existing
mechanisms of the spin dependent electron scattering. We demonstrate that the
increase of the spin orbit or spin flip electron scattering rates results in
completely different transformations of at the free F layer
interface. The developed formalism has been applied for the interpretation of
the available experimental data.Comment: 5 pages, 8 figure
Influence of magnetic impurities on charge transport in diffusive-normal-metal / superconductor junctions
Charge transport in the diffusive normal metal (DN) / insulator / - and -wave superconductor junctions is studied in the presence of magnetic
impurities in DN in the framework of the quasiclassical Usadel equations with
the generalized boundary conditions. The cases of - and d-wave
superconducting electrodes are considered. The junction conductance is
calculated as a function of a bias voltage for various parameters of the DN
metal: resistivity, Thouless energy, the magnetic impurity scattering rate and
the transparency of the insulating barrier between DN and a superconductor. It
is shown that the proximity effect is suppressed by magnetic impurity
scattering in DN for any value of the barrier transparency. In low-transparent
s-wave junctions this leads to the suppression of the normalized zero-bias
conductance. In contrast to that, in high transparent junctions zero-bias
conductance is enhanced by magnetic impurity scattering. The physical origin of
this effect is discussed. For the d-wave junctions, the dependence on the
misorientation angle between the interface normal and the crystal axis
of a superconductor is studied. The zero-bias conductance peak is suppressed by
the magnetic impurity scattering only for low transparent junctions with
. In other cases the conductance of the d-wave junctions does
not depend on the magnetic impurity scattering due to strong suppression of the
proximity effect by the midgap Andreev resonant states.Comment: 11 pages, 13 figures;d-wave case adde
Anisotropic properties of MgB2 by torque magnetometry
Anisotropic properties of superconducting MgB2 obtained by torque
magnetometry are compared to theoretical predictions, concentrating on two
issues. Firstly, the angular dependence of Hc2 is shown to deviate close to Tc
from the dependence assumed by anisotropic Ginzburg-Landau theory. Secondly,
from the evaluation of torque vs angle curves it is concluded that the
anisotropy of the penetration depth gamma_lambda has to be substantially higher
at low temperature than theoretical estimates, at least in fields higher than
0.2 T.Comment: 2 p.,2 Fig., submitted to Physica C (M2S-Rio proceedings); v2: 1 ref
adde
Effect of disorder on the far-infrared conductivity and on the microwave conductivity of two-band superconductors
We consider the far-infrared and the microwave conductivities of a two-band
superconductor with non-magnetic impurities. The strong coupling expressions
for the frequency and temperature dependent conductivity of a two-band
superconductor are developed assuming isotropic bands and interactions. Our
numerical results obtained using realistic interaction parameters for MgB
are compared with experiments on this compound. We find that the available
experimental results for the far-infrared conductivity of MgB are
consistent with multi-band superconductivity in the presence of a sufficiently
strong interband impurity scattering. On the other hand, our numerical results
for the microwave conductivity in the superconducting state indicate that the
experimental results obtained on samples with the highest transition
temperature are consistent with a low interband impurity scattering
rate but depend sensitively on the ratio of the total scattering rates in the
two bands. For the -band scattering rate not greater than
the -band scattering rate there is a single, broad,
low-temperature (at about 0.5) coherence peak in the microwave
conductivity. For =4--7 a high-temperature (at
about 0.9) coherence peak is dominant, but there is also a
low-temperature peak/shoulder resulting from the contribution of the -band
carriers to the microwave conductivity. For 1
only the high-temperature coherence peak should be observable.Comment: 11 pages, 6 figure
The importance of Opuntia in Mexico and routes of invasion and impact of Cactoblastis cactorum (Lepidoptera: Pyralidae)
This is the publisher's version, also available electronically from http://journals.fcla.edu/flaent/article/view/74992.The appearance of the cactus moth Cactoblastis cactorum in Florida has roused concern over its possible effects on the Opuntia-rich areas of Mexico and the southwestern United States. In this paper we discuss the economic importance of Opuntia in Mexico and propose a method to predict the invasion of the alien species C. cactorum. In Mexico, the products derived from Opuntia are mainly human food and fodder for livestock. Both cultivated and wild populations of Opuntia are currently used for these two purposes. By using bioclimatic modeling, we predicted the potential distribution of C. cactorum and overlaid this on the actual distribution of Opuntia species. The resulting maps indicate that the possible routes of invasion to Mexico are 1) along the northern border through Texas (most likely) and 2) via southeastern Mexico (less likely). The impacts of an invasion of C. cactorum on Opuntia products could be significant as well as being a threat to endemic species. Bioclimatic modeling can help to predict the areas of highest probability of attack and facilitate planning to mitigate future impacts
Disorder induced transition between s_+- and s_++ states in two-band superconductors
We have reexamined the problem of disorder in two-band superconductors, and
shown within the framework of the T-matrix approximation, that the suppression
of T_c can be described by a single parameter depending on the intraband and
interband impurity scattering rates. T_c is shown to be more robust against
nonmagnetic impurities than would be predicted in the trivial extension of
Abrikosov-Gor'kov theory. We find a disorder-induced transition from the
s_{\pm} state to a gapless and then to a fully gapped s_{++} state, controlled
by a single parameter -- the sign of the average coupling constant .
We argue that this transition has strong implications for experiments.Comment: 5 pages, 4 figures; suppl. material: 3 pages, 2 figures; published
versio
- …