1,919 research outputs found
Response functions of an artificial Anderson atom in the atomic limit
We consider the spin and pseudospin (charge) response functions of the
exactly soluble Anderson atom model. We demonstrate, in particular, that a
deviation from the magnetic Curie-law behaviour, appropriate for a free spin
one-half, increases with increasing asymmetry and temperature. In general,
oscillator strength is transferred from the spin degrees of freedom to the
pseudospin modes. We also consider the negative-U Anderson atom and demonstrate
that the pseudospin modes are the relevant low-energy excitations in this case.
Especially, the roles of the spin and charge excitations are interchanged upon
reversal of the intrasite Coulomb repulsion, U.Comment: 23 pages, 12 figures. Accepted for publication in J. Low Temp. Phy
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
Internal Magnus effects in superfluid 3A
Orbital angular momentum of the coherently aligned Cooper pairs in superfluid 3A is encountered by an object immersed in the condensate. We evaluate the associated quasiparticle-scattering asymmetry experienced by a negative ion; this leads to a measureable, purely quantum-mechanical reactive force deflecting the ion’s trajectory. Possible hydrodynamic Magnus effects are also discussed.Peer reviewe
Additive decomposability of functions over abelian groups
Abelian groups are classified by the existence of certain additive
decompositions of group-valued functions of several variables with arity gap 2.Comment: 17 page
Collective Oscillations of Vortex Lattices in Rotating Bose-Einstein Condensates
The complete low-energy collective-excitation spectrum of vortex lattices is
discussed for rotating Bose-Einstein condensates (BEC) by solving the
Bogoliubov-de Gennes (BdG) equation, yielding, e.g., the Tkachenko mode
recently observed at JILA. The totally symmetric subset of these modes includes
the transverse shear, common longitudinal, and differential longitudinal modes.
We also solve the time-dependent Gross-Pitaevskii (TDGP) equation to simulate
the actual JILA experiment, obtaining the Tkachenko mode and identifying a pair
of breathing modes. Combining both the BdG and TDGP approaches allows one to
unambiguously identify every observed mode.Comment: 5 pages, 4 figure
Fermions on half-quantum vortex
The spectrum of the fermion zero modes in the vicinity of the vortex with
fractional winding number is discussed. This is inspired by the observation of
the 1/2 vortex in high-temperature superconductors (Kirtley, et al, Phys. Rev.
Lett. 76 (1996) 1336). The fractional value of the winding number leads to the
fractional value of the invariant, which describes the topology of the energy
spectrum of fermions. This results in the phenomenon of the "half-crossing":
the spectrum approaches zero but does not cross it, being captured at the zero
energy level. The similarity with the phenomenon of the fermion condensation is
discussed.Comment: In revised version the discussion is extended and 4 references are
added. The paper is accepted for publication in JETP Letters. 10 pages, LaTeX
file, 3 figures are available at
ftp://boojum.hut.fi/pub/publications/lowtemp/LTL-96004.p
On the effect of variable identification on the essential arity of functions
We show that every function of several variables on a finite set of k
elements with n>k essential variables has a variable identification minor with
at least n-k essential variables. This is a generalization of a theorem of
Salomaa on the essential variables of Boolean functions. We also strengthen
Salomaa's theorem by characterizing all the Boolean functions f having a
variable identification minor that has just one essential variable less than f.Comment: 10 page
Mutation of Directed Graphs -- Corresponding Regular Expressions and Complexity of Their Generation
Directed graphs (DG), interpreted as state transition diagrams, are
traditionally used to represent finite-state automata (FSA). In the context of
formal languages, both FSA and regular expressions (RE) are equivalent in that
they accept and generate, respectively, type-3 (regular) languages. Based on
our previous work, this paper analyzes effects of graph manipulations on
corresponding RE. In this present, starting stage we assume that the DG under
consideration contains no cycles. Graph manipulation is performed by deleting
or inserting of nodes or arcs. Combined and/or multiple application of these
basic operators enable a great variety of transformations of DG (and
corresponding RE) that can be seen as mutants of the original DG (and
corresponding RE). DG are popular for modeling complex systems; however they
easily become intractable if the system under consideration is complex and/or
large. In such situations, we propose to switch to corresponding RE in order to
benefit from their compact format for modeling and algebraic operations for
analysis. The results of the study are of great potential interest to mutation
testing
Stability of multi-electron bubbles in liquid helium
The stability of multi-electron bubbles in liquid helium is investigated
theoretically. We find that multi-electron bubbles are unstable against fission
whenever the pressure is positive. It is shown that for moving bubbles the
Bernoulli effect can result in a range of pressures over which the bubbles are
stable.Comment: 7 pages, 5 figure
Half-Quantum Vortices in Thin Film of Superfluid He
Stability of a half-quantum vortex (HQV) in superfluid He has been
discussed recently by Kawakami, Tsutsumi and Machida in Phys. Rev. B {\bf 79},
092506 (2009). We further extend this work here and consider the A phase of
superfluid He confined in thin slab geometry and analyze the HQV realized
in this setting. Solutions of HQV and singly quantized singular vortex are
evaluated numerically by solving the Ginzburg-Landau (GL) equation and
respective first critical angular velocities are obtained by employing these
solutions. We show that the HQV in the A phase is stable near the boundary
between the A and A phases. It is found that temperature and magnetic
field must be fixed first in the stable region and subsequently the angular
velocity of the system should be increased from zero to a sufficiently large
value to create a HQV with sufficiently large probability. A HQV does not form
if the system starts with a fixed angular velocity and subsequently the
temperature is lowered down to the A phase. It is estimated that the
external magnetic field with strength on the order of 1 T is required to have a
sufficiently large domain in the temperature-magnetic field phase diagram to
have a stable HQV.Comment: 5 pages, 5 figure
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