1,920 research outputs found
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
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
Phase transitions in a three dimensional lattice London superconductor
We consider a three-dimensional lattice superconductor in
the London limit, with two individually conserved condensates. The problem,
generically, has two types of intercomponent interactions of different
characters. First, the condensates are interacting via a minimal coupling to
the same fluctuating gauge field. A second type of coupling is the direct
dissipationless drag represented by a local intercomponent current-current
coupling term in the free energy functional. The interplay between these two
types of interactions produces a number of physical effects not present in
previously investigated models with only one kind of
intercomponent interaction. In this work, we present a study of the phase
diagram of a superconductor which includes both of these
interactions. We study phase transitions and two types of competing paired
phases which occur in this general model: (i) a metallic superfluid phase
(where there is order only in the gauge invariant phase difference of the order
parameters), (ii) a composite superconducting phase where there is order in the
phase sum of the order parameters which has many properties of a
single-component superconductor but with a doubled value of electric charge. We
investigate the phase diagram with particular focus on what we call "preemptive
phase transitions". These are phase transitions {\it unique to multicomponent
condensates with competing topological objects}. A sudden proliferation of one
kind of topological defects may come about due to a fluctuating background of
topological defects in other sectors of the theory.Comment: 17 pages, 6 figures. Submitted to Physical Review
Perturbative Analysis of a Stationary Magnetosphere in an Extreme Black Hole Spacetime : On the Meissner-like Effect of an Extreme Black Hole
It is known that the Meissner-like effect is seen in a magnetosphere without
an electric current in black hole spacetime: no non-monopole component of
magnetic flux penetrates the event horizon if the black hole is extreme. In
this paper, in order to see how an electric current affects the Meissner-like
effect, we study a force-free electromagnetic system in a static and
spherically symmetric extreme black hole spacetime. By assuming that the
rotational angular velocity of the magnetic field is very small, we construct a
perturbative solution for the Grad-Shafranov equation, which is the basic
equation to determine a stationary, axisymmetric electromagnetic field with a
force-free electric current. Our perturbation analysis reveals that, if an
electric current exists, higher multipole components may be superposed upon the
monopole component on the event horizon, even if the black hole is extreme.Comment: 30 pages, 3 figure
Critical Behavior of the Meissner Transition in the Lattice London Superconductor
We carry out Monte Carlo simulations of the three dimensional (3D) lattice
London superconductor in zero applied magnetic field, making a detailed finite
size scaling analysis of the Meissner transition. We find that the magnetic
penetration length \lambda, and the correlation length \xi, scale as \lambda ~
\xi ~ |t|^{-\nu}, with \nu = 0.66 \pm 0.03, consistent with ordinary 3D XY
universality, \nu_XY ~ 2/3. Our results confirm the anomalous scaling dimension
of magnetic field correlations at T_c.Comment: 4 pages, 5 ps figure
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