541 research outputs found
Unconventional superconductors under rotating magnetic field II: thermal transport
We present a microscopic approach to the calculations of thermal conductivity
in unconventional superconductors for a wide range of temperatures and magnetic
fields. Our work employs the non-equilibrium Keldysh formulation of the
quasiclassical theory. We solve the transport equations using a variation of
the Brandt-Pesch-Tewordt (BPT) method, that accounts for the quasiparticle
scattering on vortices. We focus on the dependence of the thermal conductivity
on the direction of the field with the respect to the nodes of the order
parameter, and discuss it in the context of experiments aiming to determine the
shape of the gap from such anisotropy measurements. We consider quasi-two
dimensional Fermi surfaces with vertical line nodes and use our analysis to
establish the location of gap nodes in heavy fermion CeCoIn and organic
superconductor -(BEDT-TTF)Cu(NCS).Comment: 17 pages, 13 figure
Microscopic evidence for field-induced magnetism in CeCoIn
We present NMR data in the normal and superconducting states of CeCoIn
for fields close to T in the plane. Recent
experiments identified a first-order transition from the normal to
superconducting state for T, and a new thermodynamic phase below 290
mK within the superconducting state. We find that the Knight shifts of the
In(1), In(2) and the Co are discontinuous across the first-order transition and
the magnetic linewidths increase dramatically. The broadening differs for the
three sites, unlike the expectation for an Abrikosov vortex lattice, and
suggests the presence of static spin moments in the vortex cores. In the
low-temperature and high-field phase the broad NMR lineshapes suggest ordered
local moments, rather than a long wavelength quasiparticle spin density
modulation expected for an FFLO phase.Comment: 4 pages, 4 figures. to appear in Phys. Rev. Let
Supercomputer Simulations of Disk Galaxies
The time evolution of models for an isolated disk of highly flattened
galaxies of stars is investigated by direct integration of the Newtonian
equations of motion of N=30,000 identical stars over a time span of many
galactic rotations. Certain astronomical implications of the simulations to
actual disk-shaped (i.e. rapidly rotating) galaxies are explored as well.Comment: 3 pages, 2 figure Aat.sty, Aattable.sty, presented by E. Griv at the
JENAM 2000, S02, Moscow, Russia, 200
Effect of annealing on the specific heat of Ba(Fe1-xCox)2As2
We report on the effect of annealing on the temperature and field
dependencies of the low temperature specific heat of the electron-doped
Ba(FeCo)As for under-(x = 0.045), optimal- (x = 0.08)
and over-doped (x = 0.105 and 0.14) regimes. We observed that annealing
significantly improves some superconducting characteristics in
Ba(FeCo)As. It considerably increases ,
decreases in the superconducting state and suppresses the
Schottky-like contribution at very low temperatures. The improved sample
quality allows for a better identification of the superconducting gap structure
of these materials. We examine the effects of doping and annealing within a
self-consistent framework for an extended s-wave pairing scenario. At optimal
doping our data indicates the sample is fully gapped, while for both under and
overdoped samples significant low-energy excitations possibly consistent with a
nodal structure remain. The difference of sample quality offers a natural
explanation for the variation in low temperature power laws observed by many
techniques.Comment: 9 pages: added references, two figures and supplementary information;
Accepted to Physical Review B (Jan 10, 2010
Spin relaxation in quantum dots due to electron exchange with leads
We calculate spin relaxation rates in lateral quantum dot systems due to
electron exchange between dots and leads. Using rate equations, we develop a
theoretical description of the experimentally observed electric current in the
spin blockade regime of double quantum dots. Single expression fits the entire
current profile and describes the structure of both the conduction peaks and of
the suppressed (`valley') region. Extrinsic rates calculated here have to be
taken into account for accurate extraction of intrinsic relaxation rates due to
the spin-orbit and hyperfine spin scattering mechanisms from spin blockade
measurements.Comment: 4+ pages, 3 figures, submitted to PR
Anomalous Attenuation of Transverse Sound in 3He
We present the first measurements of the attenuation of transverse sound in
superfluid 3He-B. We use fixed path length interferometry combined with the
magneto-acoustic Faraday effect to vary the effective path length by a factor
of two, resulting in absolute values of the attenuation. We find that
attenuation is significantly larger than expected from the theoretical
dispersion relation, in contrast to the phase velocity of transverse sound. We
suggest that the anomalous attenuation can be explained by surface Andreev
bound states.Comment: 4 pages, 5 figures, accepted to Phys. Rev. Let
Nodal gap structure of BaFe_2(As_{1-x}P_x)_2 from angle-resolved thermal conductivity in a magnetic field
The structure of the superconducting order parameter in the iron-pnictide
superconductor BaFe(AsP) (\,K) with line
nodes is studied by the angle-resolved thermal conductivity measurements in a
magnetic field rotated within the basal plane. We find that the thermal
conductivity displays distinct fourfold oscillations with minima when the field
is directed at with respect to the tetragonal a-axis. We discuss
possible gap structures that can account for the data, and conclude that the
observed results are most consistent with the closed nodal loops located at the
flat parts of the electron Fermi surface with high Fermi velocity.Comment: 4 pages, 4 figure
Distribution of Alien Plant Species of the Middle Volga Region (South-East of the European Part of Russia): a Dataset
Background The dataset presented in the current study contains information regarding alien vascularplant species found in the Middle Volga Region (South-East of the European part ofRussia). The dataset overall includes 413 species belonging to 247 genera and 67families. The described dataset is based on the data published during floristic studies from1851 to 2019. The dataset does not include alien vascular plant species that havepresently disappeared from the territory of the region. It contains a total of 7,782 records ofoccurrences, extracted from the Salix system of information and analytics, developed in theInstitute of Ecology of the Volga River Basin of the Russian Academy of Sciences.New informationA total of 7,782 records were published on the occurrence of alien vascular plants in theMiddle Volga Region. Each entry includes information regarding the place of occurrence ofthe alien plant species, the year of occurrence, the person who recorded the alien plantand who identified it, status of the species (introduced or invasive), link to the herbarium,which contains the specimen and the literary source. If it were impossible to establish thenames of the persons who collected the samples and (or) their identification in theidentifiedBy and recordedBy fields, the names of the authors of the publication given in theassociatedReferences field were entered. The presented dataset supplements theinformation on the distribution of alien plant species in the whole European part of Russiaand specifies the places of their findings in the Middle Volga Region © Senator S et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Funding: This work was supported by the Competitiveness of the Ural Federal University (Russian Federation Government Regulation no. 211, contract no. 02. A03.21.0006)
Precipitation of the ordered α2 phase in a near-α titanium alloy
Precipitate evolution in a near-α alloy was studied using transmission electron microscopy (TEM) and correlative atom probe tomography (APT) after ageing at 550-700 for times up to 28 days. It is found that precipitation occurs much faster and is more prolific in samples heat treated at higher temperatures. Particles were spherical after ageing at 550 °C, while after ageing at 700 °C they become ellipsoids with the major axis lying close to the [0001] direction. At longer ageing times, the α2 precipitates were found to contain greater amounts of Sn + Si, indicating that Sn and Si are stronger Ti3(Al,Sn,Si) formers than Al
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