259 research outputs found
A Simple Analytical Model of Vortex Lattice Melting in 2D Superconductors
The melting of the Abrikosov vortex lattice in a 2D type-II superconductor at
high magnetic fields is studied analytically within the framework of the
phenomenological Ginzburg-Landau theory. It is shown that local phase
fluctuations in the superconducting order parameter, associated with low
energies sliding motions of Bragg chains along the principal crystallographic
axes of the vortex lattice, lead to a weak first order 'melting' transition at
a certain temperature , well below the mean field , where
the shear modulus drops abruptly to a nonzero value. The residual shear modulus
above decreases asymptotically to zero with increasing temperature.
Despite the large phase fluctuations, the average positions of Bragg chains at
fimite temperature correspond to a regular vortex lattice, slightly distorted
with respect to the triangular Abrikosov lattice. It is also shown that a
genuine long range phase coherence exists only at zero temperature; however,
below the melting point the vortex state is very close to the triangular
Abrikosov lattice. A study of the size dependence of the structure factor at
finite temperature indicates the existence of quasi-long range order with
, and , where
superconducting crystallites of correlated Bragg chains grow only along pinning
chains. This finding may suggest a very efficient way of generating pinning
defects in quasi 2D superconductors. Our results for the melting temperature
and for the entropy jump agree with the state of the art Monte Carlo
simulations.Comment: 10 pages, 4 figure
2D Weyl Fermi gas model of Superconductivity in the Surface state of a Topological Insulator at High Magnetic fields
The Nambu-Gorkov Green's function approach is applied to strongly type-II
superconductivity in a 2D spin-momentum locked (Weyl) Fermi gas model at high
perpendicular magnetic fields. When the chemical potential is sufficiently
close to the branching (Dirac) point, such that the cyclotron effective mass,
, is a very small fraction of the free electron mass, ,
relatively large portion of the phase diagram is exposed to
magneto-quantum oscillation effects. This model system is realized in the 2D
superconducting state, observed recently on the surface of the topological
insulator SbTe, for which high field measurements were reported at
low carrier densities with . Calculations of the pairing
condensation energy in such a system, as a function of and , using both
the Weyl model and a reference standard model, that exploits a simple quadratic
dispersion law, are found to yield indistinguishable results in comparison with
the experimental data. Significant deviations from the predictions of the
standard model are found only for very small carrier densities, when the
cyclotron energy becomes very large, the Landau level filling factors are
smaller than unity, and the Fermi energy shrinks below the cutoff energy.Comment: 10 page
Self-consistent Bogoliubov de Gennes theory of the vortex lattice state in a two-dimensional strong type-II superconductor at high magnetic fields
A self-consistent Bogoliubov deGennes theory of the vortex lattice state in a
2D strong type-II superconductor at high magnetic fields reveals a novel
quantum mixed state around the semiclassical Hc2, characterized by a
well-defined Landau--Bloch band structure in the quasi-particle spectrum and
suppressed order-parameter amplitude, which sharply crossover into the
well-known semiclassical (Helfand-Werthamer) results upon decreasing magnetic
field. Application to the 2D superconducting state observed recently on the
surface of the topological insulator Sb2Te3, accounts well for the experimental
data, revealing a strong type-II superconductor, with unusually low carrier
density and very small cyclotron mass, which can be realized only in the strong
coupling superconductor limit.Comment: 5 pages, 3 figure
Damping of dHvA oscillations and vortex-lattice disorder in the peak-effect region of strong type-II superconductors
The phenomenon of magnetic quantum oscillations in the superconducting state
poses several questions that still defy satisfactory answers. A key
controversial issue concerns the additional damping observed in the vortex
state. Here, we show results of \mu SR, dHvA, and SQUID magnetization
measurements on borocarbide superconductors, indicating that a sharp drop
observed in the dHvA amplitude just below H_{c2} is correlated with enhanced
disorder of the vortex lattice in the peak-effect region, which significantly
enhances quasiparticle scattering by the pair potential.Comment: 4 pages 4 figure
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