2,295 research outputs found
Differential operators and Cherednik algebras
We establish a link between two geometric approaches to the representation
theory of rational Cherednik algebras of type A: one based on a noncommutative
Proj construction, used in [GS]; the other involving quantum hamiltonian
reduction of an algebra of differential operators, used in [GG].
In the present paper, we combine these two points of view by showing that the
process of hamiltonian reduction intertwines a naturally defined geometric
twist functor on D-modules with the shift functor for the Cherednik algebra.
That enables us to give a direct and relatively short proof of the key result,
[GS, Theorem 1.4] without recourse to Haiman's deep results on the n! theorem.
We also show that the characteristic cycles defined independently in these two
approaches are equal, thereby confirming a conjecture from [GG].Comment: 37 p
Is the term "type-1.5 superconductivity" warranted by Ginzburg-Landau theory?
It is shown that within the Ginzburg-Landau (GL) approximation the order
parameters Delta1(r, T) and Delta2(r, T) in two-band superconductors vary on
the same length scale, the difference in the zero-T coherence lengths xi0_i
~vF_i/Delta_i(0), i = 1, 2 notwithstanding. This amounts to a single physical
GL parameter kappa and the classic GL dichotomy: kappa < 1/sqrt(2) for type-I
and kappa > 1/sqrt(2) for type-II.Comment: 5 pages, revised and extended version; previous title "Two-band
superconductors near Tc" change
Oscillon resonances and creation of kinks in particle collisions
We present a numerical study of the process of production of kink-antikink
pairs in the collision of particle-like states in the one-dimensional
model. It is shown that there are 3 steps in the process, the first step is to
excite the oscillon intermediate state in the particle collision, the second
step is a resonance excitation of the oscillon by the incoming perturbations,
and finally, the soliton-antisoliton pair can be created from the resonantly
excited oscillon. It is shown that the process depends fractally on the
amplitude of the perturbations and the wave number of the perturbation. We also
present the effective collective coordinate model for this process.Comment: 4 pages, 4 figures, revtex
Observation of Coherently-Enhanced Tunable Narrow-Band Terahertz Transition Radiation from a Relativistic Sub-Picosecond Electron Bunch Train
We experimentally demonstrate the production of narrow-band (% at THz) THz transition radiation with tunable
frequency over [0.37, 0.86] THz. The radiation is produced as a train of
sub-picosecond relativistic electron bunches transits at the vacuum-aluminum
interface of an aluminum converter screen. We also show a possible application
of modulated beams to extend the dynamical range of a popular bunch length
diagnostic technique based on the spectral analysis of coherent radiation.Comment: 3 pages, 6 figure
Origin of Orthorhombic Transition, Magnetic Transition, and Shear Modulus Softening in Iron Pnictide Superconductors: Analysis based on the Orbital Fluctuation Theory
The main features in iron-pnictide superconductors are summarized as (i) the
orthorhombic transition accompanied by remarkable softening of shear modulus,
(ii) high-Tc superconductivity close to the orthorhombic phase, and (iii)
stripe-type magnetic order induced by orthorhombicity. To present a unified
explanation for them, we analyze the multiorbital Hubbard-Holstein model with
Fe-ion optical phonons based on the orbital fluctuation theory. In the
random-phase-approximation (RPA), a small electron-phonon coupling constant
() is enough to produce large orbital (=charge quadrupole)
fluctuations. The most divergent susceptibility is the
-antiferro-quadrupole (AFQ) susceptibility, which causes the s-wave
superconductivity without sign reversal (s_{++}-wave state). At the same time,
divergent development of -ferro-quadrupole (FQ) susceptibility is
brought by the "two-orbiton process" with respect to the AFQ fluctuations,
which is absent in the RPA. The derived FQ fluctuations cause the softening of
shear modulus, and its long-range-order not only triggers the
orthorhombic structure transition, but also induces the instability of
stripe-type antiferro-magnetic state. In other words, the condensation of
composite bosons made of two orbitons gives rise to the FQ order and structure
transition. The theoretically predicted multi-orbital-criticality presents a
unified explanation for abovementioned features of iron pnictide
superconductors.Comment: 19 pages, 15 figure
Vortex Origin of Tricritical Point in Ginzburg-Landau Theory
Motivated by recent experimental progress in the critical regime of
high- superconductors we show how the tricritical point in a
superconductor can be derived from the Ginzburg-Landau theory as a consequence
of vortex fluctuations. Our derivation explains why usual renormalization group
arguments always produce a first-order transition, in contrast to experimental
evidence and Monte Carlo simulations.Comment: 4 pages,1 figur
Softer than normal, but not as soft as one might think: Spontaneous flux lattices in ferromagnetic spin-triplet superconductors
A theory is developed for the spontaneous vortex lattice that is expected to
occur in the ferromagnetic superconductors ZrZn_2, UGe_2, and URhGe, where the
superconductivity is likely of spin-triplet nature. The long-wavelength
fluctuations of this spontaneous flux lattice are predicted to be huge compared
to those of a conventional flux lattice, and to be the same as those for
spin-singlet ferromagnetic superconductors. It is shown that these fluctuations
lead to unambiguous experimental signatures which may provide the easiest way
to observe the spontaneous flux lattice.Comment: 4pp, 1 eps fi
Observation of a New Mechanism of Spontaneous Generation of Magnetic Flux in a Superconductor
We report the discovery of a new mechanism of spontaneous generation of a
magnetic flux in a superconductor cooled through . The sign of the
spontaneous flux changes randomly from one cooldown to the next, and follows a
Gaussian distribution. The width of the distribution increases with the size of
the temperature gradient in the sample. Our observations appear inconsistent
with the well known mechanisms of flux generation. The dependence on the
temperature gradient suggests that the flux may be generated through an
instability of the thermoelectric superconducting-normal quasiparticle
counterflow
ARPES kink is a "smoking gun" for the theory of high-Tc superconductors: dominance of the electron-phonon interaction with forward scattering peak
The ARPES spectra in high-Tc superconductors show four distinctive features
in the quasiparticle self-energy. All of them can be explained consistently by
the theory in which the electron phonon interaction (EPI) with the forward
scattering peak dominates over the Coulomb scattering. In particular, this
theory explains why there is no shift of the nodal kink at 70 meV in the
superconducting state, contrary to the clear shift of the anti-nodal
singularity at 40 meV. The theory predicts a ``knee''-like structure of the
imaginary part of the self-energy, which is phonon dominated for , and shows linear behavior for - due to the Coulomb scattering. Recent ARPES spectra give
that the EPI coupling constant is much larger than the Coulomb one. The
dip-hump structure in the spectral function comes out naturally from the
proposed theory.Comment: 5 pages, 3 figure
Asymptotic analysis of a secondary bifurcation of the one-dimensional Ginzburg-Landau equations of superconductivity
The bifurcation of asymmetric superconducting solutions from the normal solution is considered for the one-dimensional Ginzburg--Landau equations by the methods of formal asymptotics. The behavior of the bifurcating branch depends on the parameters d, the size of the superconducting slab, and , the Ginzburg--Landau parameter. The secondary bifurcation in which the asymmetric solution branches reconnect with the symmetric solution branch is studied for values of for which it is close to the primary bifurcation from the normal state. These values of form a curve in the -plane, which is determined. At one point on this curve, called the quintuple point, the primary bifurcations switch from being subcritical to supercritical, requiring a separate analysis. The results answer some of the conjectures of [A. Aftalion and W. C. Troy, Phys. D, 132 (1999), pp. 214--232]
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