1,522 research outputs found
Index theoretic characterization of d-wave superconductors in the vortex state
We employ index theoretic methods to study analytically the low energy
spectrum of a lattice d-wave superconductor in the vortex lattice state. This
allows us to compare singly quantized and doubly quantized
vortices, the first of which must always be accompanied by branch cuts.
For an inversion symmetric vortex lattice and in the presence of particle-hole
symmetry we prove an index theorem that imposes a lower bound on the number of
zero energy modes. Generic cases are constructed in which this bound exceeds
the number of zero modes of an equivalent lattice of doubly quantized vortices,
despite the identical point group symmetries. The quasiparticle spectrum around
the zero modes is doubly degenerate and exhibits a Dirac-like dispersion, with
velocities that become universal functions of in the limit of low
magnetic field. For weak particle-hole symmetry breaking, the gapped state can
be characterized by a topological quantum number, related to spin Hall
conductivity, which generally differs in the cases of the and
vortex lattices.Comment: 4 pages, 2 figures, 1 table (accepted for publication in PRL;
substantially rewritten for presentation clarity; references to quantum order
and visons omitted on referee's demand
Mixed state of a lattice d-wave superconductor
We study the mixed state in an extreme type-II lattice d-wave superconductor
in the regime of intermediate magnetic fields H_{c1} << H << H_{c2}. We analyze
the low energy spectrum of the problem dominated by nodal Dirac-like
quasiparticles with momenta near k_F=(\pm k_D,\pm k_D) and find that the
spectrum exhibits characteristic oscillatory behavior with respect to the
product of k_D and magnetic length l. The Simon-Lee scaling, predicted in this
regime, is satisfied only on average, with the magnitude of the oscillatory
part of the spectrum displaying the same 1/l dependence as its monotonous
``envelope'' part. The oscillatory behavior of the spectrum is due to the
inter-nodal interference enhanced by the singular nature of the low energy
eigenfunctions near vortices. We also study a separate problem of a single
vortex piercing an isolated superconducting grain of size L by L. Here we find
that the periodicity of the quasiparticle energy oscillations with respect to
k_D L is doubled relative to the case where the field is zero and the vortex is
absent, both such oscillatory behaviors being present at the leading order in
1/L. Finally, we review the overall features of the tunneling conductance
experiments in YBCO and BSCCO, and suggest an interpretation of the peaks at
5-20 meV observed in the tunneling local density of states in these materials.Comment: 16 pages, 11 figure
Thermodynamics of the quantum Landau-Lifshitz model
We present thermodynamics of the quantum su(1,1) Landau-Lifshitz model,
following our earlier exposition [J. Math. Phys. 50, 103518 (2009)] of the
quantum integrability of the theory, which is based on construction of
self-adjoint extensions, leading to a regularized quantum Hamiltonian for an
arbitrary n-particle sector. Starting from general discontinuity properties of
the functions used to construct the self-adjoint extensions, we derive the
thermodynamic Bethe Ansatz equations. We show that due to non-symmetric and
singular kernel, the self-consistency implies that only negative chemical
potential values are allowed, which leads to the conclusion that, unlike its
su(2) counterpart, the su(1,1) LL theory at T=0 has no instabilities.Comment: 10 page
Higher charges and regularized quantum trace identities in su(1,1) Landau-Lifshitz model
We solve the operator ordering problem for the quantum continuous integrable
su(1,1) Landau-Lifshitz model, and give a prescription to obtain the quantum
trace identities, and the spectrum for the higher-order local charges. We also
show that this method, based on operator regularization and renormalization,
which guarantees quantum integrability, as well as the construction of
self-adjoint extensions, can be used as an alternative to the discretization
procedure, and unlike the latter, is based only on integrable representations.Comment: 27 pages; misprints corrected, references adde
The intermediate evolution phase in case of truncated selection
Using methods of statistical physics, we present rigorous theoretical
calculations of Eigen's quasispecies theory with the truncated fitness
landscape which dramatically limits the available sequence space of a
reproducing quasispecies. Depending on the mutation rates, we observe three
phases, a selective one, an intermediate one with some residual order and a
completely randomized phase. Our results are applicable for the general case of
fitness landscape.Comment: 8 page
Solution of the Roth-Marques-Durian Rotational Abrasion Model
We solve the rotational abrasion model of Roth, Marques and Durian
(arXiv:1009.3492), a one-dimensional quasilinear partial differential equation
resembling the inviscid Burgers equation with the unusual feature of a step
function factor as a coefficient. The complexity of the solution is primarily
in keeping track of the cases in the piecewise function that results from
certain amputation and interpolation processes, so we also extract from it a
model of an evolving planar tree graph that tracks the evolution of the coarse
features of the contour.Comment: 5 pages, 4 figure
Fourier transform spectroscopy of d-wave quasiparticles in the presence of atomic scale pairing disorder
The local density of states power spectrum of optimally doped
BiSrCaCuO (BSCCO) has been interpreted in terms of
quasiparticle interference peaks corresponding to an "octet'' of scattering
wave vectors connecting k-points where the density of states is maximal. Until
now, theoretical treatments have not been able to reproduce the experimentally
observed weights and widths of these "octet'' peaks; in particular, the
predominance of the dispersing "q'' peak parallel to the Cu-O bond
directions has remained a mystery. In addition, such theories predict
"background'' features which are not observed experimentally. Here, we show
that most of the discrepancies can be resolved when a realistic model for the
out-of-plane disorder in BSCCO is used. Weak extended potential scatterers,
which are assumed to represent cation disorder, suppress large-momentum
features and broaden the low-energy "q''-peaks, whereas scattering at order
parameter variations, possibly caused by a dopant-modulated pair interaction
around interstitial oxygens, strongly enhances the dispersing "q''-peaks.Comment: 7 pages, 3 figure
Plasmonic modulator optimized by patterning of active layer and tuning permittivity
We study an ultra-compact plasmonic modulator that can be applied in photonic
integrated circuits. The modulator is a metal-insulator-metal waveguide with an
additional ultra-thin layer of indium tin oxide (ITO). Bias is applied to the
multilayer core by means of metal plates that serve as electrodes. External
field changes carrier density in the ultra-thin ITO layer, which influences the
permittivity. The metal-insulator-metal system possesses a plasmon resonance,
and it is strongly affected by changes in the permittivity of the active layer.
To improve performance of the structure we propose several optimizations. We
examine influence of the ITO permittivity on the modulator's performance and
point out appropriate values. We analyze eigenmodes of the waveguide structure
and specify the range for its efficient operation. We show that substituting
the continuous active layer by a one-dimension periodic stripes increases
transmittance through the device and keeps the modulator's performance at the
same level. The dependence on the pattern size and filling factor of the active
material is analyzed and optimum parameters are found. Patterned ITO layers
allow us to design a Bragg grating inside the waveguide. The grating can be
turned on and off, thus modulating reflection from the structure. The
considered structure with electrical control possesses a high performance and
can efficiently work as a plasmonic component in nanophotonic architectures.Comment: Optics Communications (2012
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