452 research outputs found
Motion of vortices in ferromagnetic spin-1 BEC
The paper investigates dynamics of nonsingular vortices in a ferromagnetic
spin-1 BEC, where spin and mass superfluidity coexist in the presence of
uniaxial anisotropy (linear and quadratic Zeeman effect). The analysis is based
on hydrodynamics following from the Gross-Pitaevskii theory. Cores of
nonsingular vortices are skyrmions with charge, which is tuned by uniaxial
anisotropy and can have any fractal value between 0 and 1. There are
circulations of mass and spin currents around these vortices. The results are
compared with the equation of vortex motion derived earlier in the
Landau-Lifshitz-Gilbert theory for magnetic vortices in easy-plane
ferromagnetic insulators. In the both cases the transverse gyrotropic force
(analog of the Magnus force in superfluid and classical hydrodynamics) is
proportional to the charge of skyrmions in vortex cores.Comment: 19 pages, 2 figures, to be published in the special issue of Fizika
Nizkikh Temperatur dedicated to A.M.Kosevich. arXiv admin note: substantial
text overlap with arXiv:1801.0109
Mechanical measurement of equilibrium spin currents in the Rashba medium
We demonstrate that an equilibrium spin current in a 2D electron gas with
Rashba spin-orbit interaction (Rashba medium) results in a mechanical torque on
a substrate near an edge of the medium. If the substrate is a cantilever, the
mechanical torque displaces the free end of the cantilever. The effect can be
enhanced and tuned by a magnetic field. Observation of this displacement would
be an effective method to prove existence of equilibrium spin currents. The
analysis of edges of the Rashba medium demonstrates the existence of localized
edge states. They form a 1D continuum of states. This suggests a new type of
quantum wire: spin-orbit quantum wire.Comment: 4 pages, 1 figur
Domain structure of superconducting ferromagnets
In superconducting ferromagnets the equilibrium domain structure is absent in
the Meissner state, but appears in the spontaneous vortex phase (the mixed
state in zero external magnetic field), though with a period, which can
essentially exceed that in normal ferromagnets. Metastable domain walls are
possible even in the Meissner state. The domain walls create magnetostatic
fields near the sample surface, which can be used for experimental detection of
domain walls.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Let
The Dynamic Structure Factor of the 1D Bose Gas near the Tonks-Girardeau Limit
While the 1D Bose gas appears to exhibit superfluid response under certain
conditions, it fails the Landau criterion according to the elementary
excitation spectrum calculated by Lieb. The apparent riddle is solved by
calculating the dynamic structure factor of the Lieb-Liniger 1D Bose gas. A
pseudopotential Hamiltonian in the fermionic representation is used to derive a
Hartree-Fock operator, which turns out to be well-behaved and local. The
Random-Phase approximation for the dynamic structure factor based on this
derivation is calculated analytically and is expected to be valid at least up
to first order in , where is the dimensionless interaction
strength of the model. The dynamic structure factor in this approximation
clearly indicates a crossover behavior from the non-superfluid Tonks to the
superfluid weakly-interacting regime, which should be observable by Bragg
scattering in current experiments.Comment: 4 pages, 2 figures misprints in formulas correcte
Comment on "Domain Structure in a Superconducting Ferromagnet"
According to Faure and Buzdin [Phys. Rev. Lett. 94, 187202 (2005)], in a
superconducting ferromagnet a domain structure with a period small compared
with the London penetration depth can arise. They claim that this contradicts
to the conclusion of Sonin [Phys. Rev. B, 66, 100504 (2002)] that ferromagnetic
domain structure in the Meissner state of a superconducting ferromagnet is
absent in equilibrium. This contradiction is imaginary, based on
misinterpretation of the results of these two papers.Comment: 1 page, no figures, final version published in Phys.Rev.Let
Equilibrium rotation of a vortex bundle terminating on a lateral wall
The paper investigates possibility of equilibrium solid-body rotation of a
vortex bundle diverging at some height from a cylinder axis and terminating on
a lateral wall of a container. Such a bundle arises when vorticity expands up
from a container bottom eventually filling the whole container. The analysis
starts from a single vortex, then goes to a vortex sheet, and finally addresses
a multi-layered crystal vortex bundle. The equilibrium solid-body rotation of
the vortex bundle requires that the thermodynamic potentials in the
vortex-filled and in the vortex-free parts of the container are equal providing
the absence of a force on the vortex front separating the two parts. The paper
considers also a weakly non-equilibrium state when the bundle and the container
rotate with different angular velocities and the vortex front propagates with
the velocity determined by friction between vortices and the container or the
normal liquid moving together with the container.Comment: 16 pages, 5 figure
Ground State and Tkachenko Modes of a Rapidly Rotating Bose-Einstein Condensate in the Lowest Landau Level State
The Letter considers the ground state and the Tkachenko modes for a rapidly
rotating Bose-Einstein condensate (BEC), when its macroscopic wave function is
a coherent superposition of states analogous to the lowest Landau levels of a
charge in a magnetic field. As well as in type II superconductors close to the
critical magnetic field , this corresponds to a periodic vortex
lattice. The exact value of the shear elastic modulus of the vortex lattice,
which was known from the old works on type II superconductors, essentially
exceeds the values calculated recently for BEC. This is important for
comparison with observation of the Tkachenko mode in the rapidly rotating BEC.Comment: 5 pages, 1 figure; discussion edited, references added, numerical
factors and typos correcte
Superconductor-metal transition in an ultrasmall Josephson junction biased by a noisy voltage source
Shot noise in a voltage source changes the character of the quantum
(dissipative) phase transition in an ultrasmall Josephson junction: The
superconductor-insulator transition transforms into the superconductor-metal
transition. In the metallic phase the IV curve probes the voltage distribution
generated by shot noise, whereas in the superconducting phase it probes the
counting statistics of electrons traversing the noise junction.Comment: 4 pages, 3 figures. Corrected typos and style, added reference
Superfluidity in a gas of strongly-interacting bosons
We consider small systems of bosonic atoms rotating in a toroidal trap. Using
the method of exact numerical diagonalization of the many-body Hamiltonian, we
examine the transition from the Bose-Einstein condensed state to the
Tonks-Girardeau state. The system supports persistent currents in a wide range
between the two limits, even in the absence of Bose-Einstein condensation.Comment: 7 pages, 3 figures, revised version, to appear in Europh. Let
Domain wall superconductivity in superconductor/ferromagnet bilayers
We analyze the enhancement of the superconducting critical temperature of
superconducting/ferromagnetic bilayers due to the appearance of localized
superconducting states in the vicinity of magnetic domain walls in the
ferromagnet. We consider the case when the main mechanism of the
superconductivity destruction via the proximity effect is the exchange field.
We demonstrate that the influence of the domain walls on the superconducting
properties of the bilayer may be quite strong if the domain wall thickness is
of the order of superconducting coherence length.Comment: 8 pages, 2 figure
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