934 research outputs found
Surface melting of the vortex lattice
We discuss the effect of an (ab)-surface on the melting transition of the
pancake-vortex lattice in a layered superconductor within a density functional
theory approach. Both discontinuous and continuous surface melting are
predicted for this system, although the latter scenario occupies the major part
of the low-field phase diagram. The formation of a quasi-liquid layer below the
bulk melting temperature inhibits the appearance of a superheated solid phase,
yielding an asymmetric hysteretic behavior which has been seen in experiments.Comment: 4 pages, 3 figure
Density functional theory of vortex lattice melting in layered superconductors: a mean-field--substrate approach
We study the melting of the pancake vortex lattice in a layered
superconductor in the limit of vanishing Josephson coupling. Our approach
combines the methodology of a recently proposed mean-field substrate model for
such systems with the classical density functional theory of freezing. We
derive a free-energy functional in terms of a scalar order-parameter profile
and use it to derive a simple formula describing the temperature dependence of
the melting field. Our theoretical predictions are in good agreement with
simulation data. The theoretical framework proposed is thermodynamically
consistent and thus capable of describing the negative magnetization jump
obtained in experiments. Such consistency is demonstrated by showing the
equivalence of our expression for the density discontinuity at the transition
with the corresponding Clausius-Clapeyron relation.Comment: 11 pages, 4 figure
Surface Melting of the Vortex Lattice in Layered Superconductors: Density Functional Theory
We study the effects of an -surface on the vortex-solid to vortex-liquid
transition in layered superconductors in the limit of vanishing inter-layer
Josephson coupling. We derive the interaction between pancake vortices in a
semi-infinite sample and adapt the density functional theory of freezing to
this system. We obtain an effective one-component order-parameter theory which
can be used to describe the effects of the surface on vortex-lattice melting.
Due to the absence of protecting layers in the neighbourhood of the surface,
the vortex lattice formed near the surface is more susceptible to thermal
fluctuations. Depending on the value of the magnetic field, we predict either a
continuous or a discontinuous surface melting transition. For intermediate
values of the magnetic field, the surface melts continuously, assisting the
formation of the liquid phase and suppressing hysteresis above the melting
transition, a prediction consistent with experimental results. For very low and
very high magnetic fields, the surface melts discontinuously. The two different
surface melting scenarios are separated by two surface multicritical points,
which we locate on the melting line.Comment: 16 pages, 12 figure
Dissociation of vortex stacks into fractional-flux vortices
We discuss the zero field superconducting phase transition in a finite system
of magnetically coupled superconducting layers. Transverse screening is
modified by the presence of other layers resulting in topological excitations
with fractional flux. Vortex stacks trapping a full flux and present at any
finite temperature undergo an evaporation transition which corresponds to the
depairing of fractional-flux vortices in individual layers. We propose an
experiment with a bi-layer system allowing us to identify the dissociation of
bound vortex molecules.Comment: 4 pages, 1 figure; revised version, to appear in Phys. Rev. Let
The ISCIP Analyst, Volume II, Issue 5
This repository item contains a single issue of The ISCIP Analyst, an analytical review journal published from 1996 to 2010 by the Boston University Institute for the Study of Conflict, Ideology, and Policy
The ISCIP Analyst, Volume II, Issue 14
This repository item contains a single issue of The ISCIP Analyst, an analytical review journal published from 1996 to 2010 by the Boston University Institute for the Study of Conflict, Ideology, and Policy
The ISCIP Analyst, Volume II, Issue 15
This repository item contains a single issue of The ISCIP Analyst, an analytical review journal published from 1996 to 2010 by the Boston University Institute for the Study of Conflict, Ideology, and Policy
Harmonic Potential Theorem: Extension to Spin-, Velocity-, and Density-Dependent Interactions
One of the few exact results for the description of the time evolution of an inhomogeneous, interacting many-particle system is given by the harmonic potential theorem (HPT). The relevance of this theorem is that it sets a tight constraint on time-dependent many-body approximations. In this contribution, we show that the original formulation of the HPT is valid also for the case of spin-, velocity-, and density-dependent interactions. This result is completely general and relevant, among the rest, for nuclear structure theory both in the case of ab initio and of more phenomenological approaches. As an example, we report on a numerical implementation by testing the small-amplitude limit of the time-dependent Hartree-Fock-also known as the random phase approximation-for the translational frequencies of a neutron system trapped in a harmonic potential
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