712 research outputs found
Comment on ``Quasiparticle Spectra around a Single Vortex in a d-wave Superconductor''
In a recent Letter Morita, Kohmoto and Maki analyzed the structure of
quasiparticle states near a single vortex in a d-wave superconductor using an
approximate version of the Bogoliubov - de Gennes theory. Their principal
result is the existence of a bound state within the core region at finite
energy with full rotational symmetry, which they assert explains the recent
scanning tunneling microscopy results on YBCO single crystals. Here we argue
that the approximation used in this work is fundamentally inadequate for the
description of a d-wave vortex and that the obtained circular symmetry of the
local density of states is an unphysical artifact of this approximation.Comment: 1 page REVTeX, to appear in PR
Elastic precession of electronic spin states in interacting integer quantum Hall edge channels
We consider the effect of Coulomb interactions in the propagation of
electrons, prepared in arbitrary spin states, on chiral edge channels in the
integer quantum Hall regime. Electrons are injected and detected at the same
energy at different locations of the Hall bar, which is modeled as a chiral
Tomonaga-Luttinger liquid. The current is computed perturbatively in the
tunneling amplitudes, within a non-crossing approximation using exact solutions
of the interacting Green's functions. In the case of different channel
velocities, the spin precession effect is evaluated, and the role of
interaction parameters and wavevectors is discussed.Comment: 5 pages, 3 figure
Violation of the Wiedemann-Franz Law in a Large-N Solution of the t-J Model
We show that the Wiedemann-Franz law, which holds for Landau Fermi liquids,
breaks down in a large-n treatment of the t-J model. The calculated ratio of
the in-plane thermal and electrical conductivities agrees quantitatively with
experiments on the normal state of the electron-doped Pr_{2-x}Ce_xCuO_4 (x =
0.15) cuprate superconductor. The violation of the Wiedemann-Franz law in the
uniform phase contrasts with other properties of the phase that are Fermi
liquid like.Comment: 4 pages, 2 figures. Typos corrected, one added reference, revised
discussion of experiment on 214 cuprate material (x = 0.06
Reversible switch from hemoglobin A to C in sheep and recovery from anemia following experimental infection with Anaplasma ovis
Anemia causes a change in the type of circulating hemoglobin (Hb) in sheep carrying the βA-globin haplotype, where the Hb A is replaced with Hb C, unlike Hb B. The effect of the substitution of Hb A with Hb C on the recovery from anemia was investigated by comparing the hematological picture of sheep, following experimental infection with Anaplasma ovis. The blood values were obtained from 3 AB and 3 BB Hb sheep after the development of the disease where anemia is a pathognomonic symptom. The expression of the silent gene encoding for Hb C was detected by isoelectric focusing and quantified by high performance liquid chromatography. Both Hb AB genotype and Hb C occurrence were involved in the lower recovery from anemia in the trial
Coherent manipulation of charge qubits in double quantum dots
The coherent time evolution of electrons in double quantum dots induced by
fast bias-voltage switches is studied theoretically. As it was shown
experimentally, such driven double quantum dots are potential devices for
controlled manipulation of charge qubits. By numerically solving a quantum
master equation we obtain the energy- and time-resolved electron transfer
through the device which resembles the measured data. The observed oscillations
are found to depend on the level offset of the two dots during the manipulation
and, most surprisingly, also the on initialization stage. By means of an
analytical expression, obtained from a large-bias model, we can understand the
prominent features of these oscillations seen in both the experimental data and
the numerical results. These findings strengthen the common interpretation in
terms of a coherent transfer of electrons between the dots.Comment: 18 pages, 4 figure
Two-state behaviour of Kondo trimers
The electronic properties and spectroscopic features of a magnetic trimer
with a Kondo-like coupling to a non-magnetic metallic substrate are analyzed at
zero temperature. The substrate density of states is depressed in the trimer
neighbourhood, being exactly zero at the substrate chemical potential. The size
of the resonance strongly depends on the magnetic state of the trimer, and
exhibits a two-state behavior. The geometrical dependence of these results
agree qualitatively with recent experiments and could be reproduced in a
triangular quantum dot arrangement.Comment: 5 pages, including 4 figure
Specific heat of single crystal MgB_2: a two-band superconductor with two different anisotropies
Heat-capacity measurements of a 39 microgramm MgB_2 single crystal in fields
up to 14 T and below 3 K allow the determination of the low-temperature linear
term of the specific heat, its field dependence and its anisotropy. Our results
are compatible with two-band superconductivity, the band carrying the small gap
being isotropic, that carrying the large gap having an anisotropy of ~ 5. Three
different upper critical fields are thus needed to describe the superconducting
state of MgB2.Comment: 4 pages, 4 figures - V2: Bibliography updated and some typo
corrected. One reference added - V3: version accepted for publication in PRL,
changes made in the tex
Theory of vortex excitation imaging via an NMR relaxation measurement
The temperature dependence of the site-dependent nuclear spin relaxation time
T_1 around vortices is studied in s-wave and d-wave superconductors.Reflecting
low energy electronic excitations associated with the vortex core, temperature
dependences deviate from those of the zero-field case, and T_1 becomes faster
with approaching the vortex core. In the core region, T_1^{-1} has a new peak
below T_c. The NMR study by the resonance field dependence may be a new method
to prove the spatial resolved vortex core structure in various superconductors.Comment: 5 pages, 3 figure
Electromagnetic response of a static vortex line in a type-II superconductor : a microscopic study
The electromagnetic response of a pinned Abrikosov fluxoid is examined in the
framework of the Bogoliubov-de Gennes formalism. The matrix elements and the
selection rules for both the single photon (emission - absorption) and two
photon (Raman scattering) processes are obtained. The results reveal striking
asymmetries: light absorption by quasiparticle pair creation or single
quasiparticle scattering can occur only if the handedness of the incident
radiation is opposite to that of the vortex core states. We show how these
effects will lead to nonreciprocal circular birefringence, and also predict
structure in the frequency dependence of conductivity and in the differential
cross section of the Raman scattering.Comment: 14 pages (RevTex
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