4,629 research outputs found
Non-Meissner electrodynamics and knotted solitons in two-component superconductors
I consider electrodynamics and the problem of knotted solitons in
two-component superconductors. Possible existence of knotted solitons in
multicomponent superconductors was predicted several years ago. However their
basic properties and stability in these systems remains an outstandingly
difficult question both for analytical and numerical treatment. Here I propose
a new perturbative approach to treat self-consistently all the degrees of
freedom in the problem. I show that there exists a length scale for a Hopfion
texture where the electrodynamics of a two-component superconductor is
dominated by a self-induced Faddeev term, which is a stark contrast to the
Meissner electrodynamics of single-component systems. I also show that at
certain short length scales knotted solitons in two-component Ginzburg-Landau
model are not described by a Faddeev-Skyrme-type model and are unstable.
However these solitons can be stable at some intermediate length scales. I
argue that configurations with a high topological charge may be more stable in
this system than low-topological-charge configurations. In the second part of
the paper I discuss qualitatively different physics of the stability of knotted
solitons in a more general Ginzburg-Landau model and point out the physically
relevant terms which enhance or suppress stability of the knotted solitons.
With this argument it is demonstrated that the generalized Ginburg-Landau model
possesses stable knotted solitons.Comment: In print in Phys. Rev. B. v2: a typo (missing factor) fixed. v3:
discussion of some aspects made more detailed following a referee reques
Hidden vortex lattices in a thermally paired superfluid
We study the evolution of rotational response of a hydrodynamic model of a
two-component superfluid with a non-dissipative drag interaction, as the system
undergoes a transition into a paired phase at finite temperature. The
transition manifests itself in a change of (i) vortex lattice symmetry, and
(ii) nature of vortex state. Instead of a vortex lattice, the system forms a
highly disordered tangle which constantly undergoes merger and reconnecting
processes involving different types of vortices, with a "hidden" breakdown of
translational symmetry.Comment: 4 pages, 5 figs. Submitted to Physical Review. Online suppl. material
available; Ref. 6. V2: Fig. 1 re-sent, URL in Ref. 6 correcte
Phase structure and phase transitions in a three dimensional SU(2) superconductor
We study the three dimensional SU(2)-symmetric noncompact CP1 model, with two
charged matter fields coupled minimally to a noncompact Abelian gauge-field.
The phase diagram and the nature of the phase transitions in this model have
attracted much interest after it was proposed to describe an unusual continuous
transition associated with deconfinement of spinons. Previously, it has been
demonstrated for various two-component gauge theories that weakly first-order
transitions may appear as continuous ones of a new universality class in
simulations of relatively large, but finite systems. We have performed
Monte-Carlo calculations on substantially larger systems sizes than those in
previous works. We find that in some area of the phase diagram where at finite
sizes one gets signatures consistent with a single first-order transition, in
fact there is a sequence of two phase transitions with an O(3) paired phase
sandwiched in between. We report (i) a new estimate for the location of a
bicritical point and (ii) the first resolution of bimodal distributions in
energy histograms at relatively low coupling strengths. We perform a flowgram
analysis of the direct transition line with rescaling of the linear system size
in order to obtain a data collapse. The data collapses up to coupling constants
where we find bimodal distributions in energy histograms.Comment: 16 pages, 11 figures. Submitted to Physical Review
Skyrmions induced by dissipationless drag in U(1)xU(1) superconductors
Rather generically, multicomponent superconductors and superfluids have
intercomponent current-current interaction. We show that in superconductors
with substantially strong intercomponent drag interaction, the topological
defects which form in external field are characterized by a skyrmionic
topological charge. We then demonstrate that they can be distinguished from
ordinary vortex matter by a very characteristic magnetization process due to
the dipolar nature of inter-skyrmion forces. The results provide an
experimental signature to confirm or rule out the formation -wave state with
reduced spin stiffness in -wave superconductors.Comment: Replaced with a version in print in Physical Review B; Improved and
extended as compared to the first version; 13 pages; 12 figure
Semi-Meissner state and neither type-I nor type-II superconductivity in multicomponent systems
Traditionally, superconductors are categorized as type-I or type-II. Type-I
superconductors support only Meissner and normal states, while type-II
superconductors form magnetic vortices in sufficiently strong applied magnetic
fields. Recently there has been much interest in superconducting systems with
several species of condensates, in fields ranging from Condensed Matter to High
Energy Physics. Here we show that the type-I/type-II classification is
insufficient for such multicomponent superconductors. We obtain solutions
representing thermodynamically stable vortices with properties falling outside
the usual type-I/type-II dichotomy, in that they have the following features:
(i) Pippard electrodynamics, (ii) interaction potential with long-range
attractive and short-range repulsive parts, (iii) for an n-quantum vortex, a
non-monotonic ratio E(n)/n where E(n) is the energy per unit length, (iv)
energetic preference for non-axisymmetric vortex states, "vortex molecules".
Consequently, these superconductors exhibit an emerging first order transition
into a "semi-Meissner" state, an inhomogeneous state comprising a mixture of
domains of two-component Meissner state and vortex clusters.Comment: in print in Phys. Rev. B Rapid Communications. v2: presentation is
made more accessible for a general reader. Latest updates and links to
related papers are available at the home page of one of the authors:
http://people.ccmr.cornell.edu/~egor
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