306 research outputs found
Vortex Lattice Structural Transitions: a Ginzburg-Landau Model Approach
We analyze the rhombic to square vortex lattice phase transition in
anisotropic superconductors using a variant of Ginzburg-Landau (GL) theory. The
mean-field phase diagram is determined to second order in the anisotropy
parameter, and shows a reorientation transition of the square vortex lattice
with respect to the crystal lattice. We then derive the long-wavelength elastic
moduli of the lattices, and use them to show that thermal fluctuations produce
a reentrant rhombic to square lattice transition line, similar to recent
studies which used a nonlocal London model.Comment: 4 pages, 3 figures, final version with various referee suggested
modifications, scheduled to appear in PR
Tunneling between bilayer quantum Hall structures in a strong magnetic field
We calculate the tunneling current in a quantum Hall bilayer system in the
strong magnetic field limit. We model the bilayer electron system as two Wigner
crystals coupled through interlayer Coulomb interactions, treated in the
continuum limit. We generalized the Johansson and Kinaret (JK) model and were
able to study the effect of the low energy out-of-phase magnetophonon modes
produced as a result of tunneling events. We find the same scaling behavior of
the tunneling current peak with the magnetic field as found by JK but were able
to find the tunneling current scaling behavior with interlayer distance as
well.Comment: 4 pages, 1 figure, SemiMag16 conference paper to be published in
International Journal of Modern Physics
Spontaneous Spin Polarization in Quantum Wires
A number of recent experiments report spin polarization in quantum wires in
the absence of magnetic fields. These observations are in apparent
contradiction with the Lieb-Mattis theorem, which forbids spontaneous spin
polarization in one dimension. We show that sufficiently strong interactions
between electrons induce deviations from the strictly one-dimensional geometry
and indeed give rise to a ferromagnetic ground state in a certain range of
electron densities.Comment: 4 pages, 4 figure
Quasiparticle mirages in the tunneling spectra of d-wave superconductors
We illustrate the importance of many-body effects in the Fourier transformed
local density of states (FT-LDOS) of d-wave superconductors from a model of
electrons coupled to an Einstein mode with energy Omega_0. For bias energies
significantly larger than Omega_0 the quasiparticles have short lifetimes due
to this coupling, and the FT-LDOS is featureless if the electron-impurity
scattering is treated within the Born approximation. In this regime it is
important to include boson exchange for the electron-impurity scattering which
provides a `step down' in energy for the electrons and allows for long
lifetimes. This many-body effect produces qualitatively different results,
namely the presence of peaks in the FT-LDOS which are mirrors of the
quasiparticle interference peaks which occur at bias energies smaller than ~
Omega_0. The experimental observation of these quasiparticle mirages would be
an important step forward in elucidating the role of many-body effects in
FT-LDOS measurements.Comment: revised text with new figures, to be published, Phys Rev
Formation of defects in multirow Wigner crystals
We study the structural properties of a quasi-one-dimensional classical
Wigner crystal, confined in the transverse direction by a parabolic potential.
With increasing density, the one-dimensional crystal first splits into a zigzag
crystal before progressively more rows appear. While up to four rows the ground
state possesses a regular structure, five-row crystals exhibit defects in a
certain density regime. We identify two phases with different types of defects.
Furthermore, using a simplified model, we show that beyond nine rows no stable
regular structures exist.Comment: 11 pages, 8 figure
Exchange Coupling in a One-Dimensional Wigner Crystal
We consider a long quantum wire at low electron densities. In this strong
interaction regime a Wigner crystal may form, in which electrons comprise an
antiferromagnetic Heisenberg spin chain. The coupling constant J is
exponentially small, as it originates from tunneling of two neighboring
electrons through the segregating potential barrier. We study this exponential
dependence, properly accounting for the many-body effects and the finite width
of the wire.Comment: 4 pages, 3 figure
Magnetic penetration depth in disordered iron-based superconductors
We study the effect of disorder on the London penetration depth in iron-based
superconductors. The theory is based on a two-band model with
quasi-two-dimensional Fermi surfaces, which allows for the coexistence region
in the phase diagram between magnetic and superconducting states in the
presence of intraband and interband scattering. Within the quasiclassical
approximation we derive and solve Eilenberger's equations, which include a weak
external magnetic field, and provide analytical expressions for the penetration
depth in the various limiting cases. A complete numerical analysis of the
doping and temperature dependence of the London penetration depth reveals the
crucial effect of disorder scattering, which is especially pronounced in the
coexistence phase. The experimental implications of our results are discussed.Comment: 10 pages, 6 figure
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