2,825 research outputs found
Robust superfluid phases of 3He in aerogel
Within a phenomenological approach possible forms of the order parameter of
the superfluid phases of 3He in a vicinity of the transition temperature are
discussed. Effect of aerogel is described by a random tensor field interacting
with the orbital part of the order parameter. With respect to their interaction
with the random tensor field a group of "robust" order parameters which can
maintain long-range order in a presence of the random field is specified.
Robust order parameters, corresponding to Equal Spin Pairing (ESP) states are
found and proposed as candidates for the observed A-like superfluid phase of
liquid 3He in aerogel.Comment: 5 pages, prepared for QFS 200
Photoluminescence of tetrahedral quantum-dot quantum wells
Taking into account the tetrahedral shape of a quantum dot quantum well
(QDQW) when describing excitonic states, phonon modes and the exciton-phonon
interaction in the structure, we obtain within a non-adiabatic approach a
quantitative interpretation of the photoluminescence (PL) spectrum of a single
CdS/HgS/CdS QDQW. We find that the exciton ground state in a tetrahedral QDQW
is bright, in contrast to the dark ground state for a spherical QDQW.Comment: 4 pages, 2 figure
Applications of BGP-reflection functors: isomorphisms of cluster algebras
Given a symmetrizable generalized Cartan matrix , for any index , one
can define an automorphism associated with of the field of rational functions of independent indeterminates It is an isomorphism between two cluster algebras associated to the
matrix (see section 4 for precise meaning). When is of finite type,
these isomorphisms behave nicely, they are compatible with the BGP-reflection
functors of cluster categories defined in [Z1, Z2] if we identify the
indecomposable objects in the categories with cluster variables of the
corresponding cluster algebras, and they are also compatible with the
"truncated simple reflections" defined in [FZ2, FZ3]. Using the construction of
preprojective or preinjective modules of hereditary algebras by Dlab-Ringel
[DR] and the Coxeter automorphisms (i.e., a product of these isomorphisms), we
construct infinitely many cluster variables for cluster algebras of infinite
type and all cluster variables for finite types.Comment: revised versio
Nucleation of superconductivity in mesoscopic star-shaped superconductors
We study the phase transition of a star-shaped superconductor, which covers
smoothly the range from zero to two dimensions with respect to the
superconducting coherence length. Detailed measurements and numerical
calculations show that the nucleation of superconductivity in this device is
very inhomogeneous, resulting in rich structure in the superconducting
transition as a function of temperature and magnetic field. The superconducting
order parameter is strongly enhanced and mostly robust in regions close to
multiple boundaries.Comment: 4 pages, 5 figures, E-mail addresses:
[email protected] (V. Chandrasekhar), [email protected]
(J. T. Devreese
A study of Schwinger-Dyson Equations for Yukawa and Wess-Zumino Models
We study Schwinger-Dyson equation for fermions in Yukawa and Wess-Zumino
models, in terms of dynamical mass generation and the wavefunction
renormalization function. In the Yukawa model with -type interaction
between scalars and fermions, we find a critical coupling in the quenched
approximation above which fermions acquire dynamical mass. This is shown to be
true beyond the bare 3-point vertex approximation. In the Wess-Zumino model,
there is a neat cancellation of terms leading to no dynamical mass for
fermions. We comment on the conditions under which these results are general
beyond the rainbow approximation and also on the ones under which supersymmetry
is preserved and the scalars as well do not acquire mass. The results are in
accordance with the non-renormalization theorem at least to order in
perturbation theory. In both the models, we also evaluate the wavefunction
renormalization function, analytically in the neighbourhood of the critical
coupling and numerically, away from it.Comment: 12 pages and 7 Postscript figures, accepted for publication in
Journal of Physics G: Nuclear and Particle Physic
Cluster algebras in algebraic Lie theory
We survey some recent constructions of cluster algebra structures on
coordinate rings of unipotent subgroups and unipotent cells of Kac-Moody
groups. We also review a quantized version of these results.Comment: Invited survey; to appear in Transformation Group
NMR in Superfluid A-like Phase of He Confined in Globally Deformed Aerogel in Tilted Magnetic Field
NMR spectra in superfluid A-like phases confined in axially deformed aerogel
in presence of a magnetic field inclined with respect to deformation axis is
considered. The characteristic features of dipole frequency shift in axially
compressed and axially stretched cases are compared. In particular, it is shown
that in axially stretched aerogel environment the stability region of
coherently spin precessing mode is rather narrow due to the U(1)LIM effect.Comment: 8 pages, 2 figure
Vortex states in superconducting rings
The superconducting state of a thin superconducting disk with a hole is
studied within the non-linear Ginzburg-Landau theory in which the
demagnetization effect is accurately taken into account. We find that the flux
through the hole is not quantized, the superconducting state is stabilized with
increasing size of the hole for fixed radius of the disk, and a transition to a
multi-vortex state is found if the disk is sufficiently large. Breaking the
circular summetry through a non central location of the hole in the disk
enhances the multi-vortex state.Comment: 11 pages, 23 figures (postscript). To appear in Physical Review B,
Vol. 61 (2000
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