300,902 research outputs found
Local Lattice Instability and Superconductivity in LaSrCuMO (M=Mn, Ni, and Co)
Local lattice structures of LaSrCuMO (M=Mn,
Ni, and Co) single crystals are investigated by polarized extended x-ray
absorption fine structure (EXAFS). The local lattice instability at low
temperature is described by in-plane Cu-O bond splitting. We find that
substitution of Mn for Cu causes little perturbation of local lattice
instability while Ni and Co substitution strongly suppresses the instability.
The suppression of superconductivity by Cu-site substitution is related to the
perturbation of lattice instability, indicating that local lattice instability
(polaron) plays an important role in superconductivity
Wigner crystal and bubble phases in graphene in the quantum Hall regime
Graphene, a single free-standing sheet of graphite with honeycomb lattice
structure, is a semimetal with carriers that have linear dispersion. A
consequence of this dispersion is the absence of Wigner crystallization in
graphene, since the kinetic and potential energies both scale identically with
the density of carriers. We study the ground state of graphene in the presence
of a strong magnetic field focusing on states with broken translational
symmetry. Our mean-field calculations show that at integer fillings a uniform
state is preferred, whereas at non-integer filling factors Wigner crystal
states (with broken translational symmetry) have lower energy. We obtain the
phase diagram of the system. We find that it is qualitatively similar to that
of quantum Hall systems in semiconductor heterostructures. Our analysis
predicts that non-uniform states, including Wigner crystal state, will occur in
graphene in the presence of a magnetic field and will lead to anisotropic
transport in high Landau levels.Comment: New references added; 9 pages, 9 figures, (paper with high-resolution
images is available at http://www.physics.iupui.edu/yogesh/graphene.pdf
Geometry and Representations of the Quantum Supergroup OSPq(1|2n)
The quantum supergroup OSPq(1|2n) is studied systematically. A Haar
functional is constructed, and an algebraic version of the Peter - Weyl theory
is extended to this quantum supergroup. Quantum homogeneous superspaces and
quantum homogeneous supervector bundles are defined following the strategy of
Connes' theory. Parabolic induction is developed by employing the quantum
homogeneous supervector bundles. Quantum Frobenius reciprocity and a
generalized Borel - Weil theorem are established for the induced
representations.Comment: Latex, 20 page
Solving Functional Constraints by Variable Substitution
Functional constraints and bi-functional constraints are an important
constraint class in Constraint Programming (CP) systems, in particular for
Constraint Logic Programming (CLP) systems. CP systems with finite domain
constraints usually employ CSP-based solvers which use local consistency, for
example, arc consistency. We introduce a new approach which is based instead on
variable substitution. We obtain efficient algorithms for reducing systems
involving functional and bi-functional constraints together with other
non-functional constraints. It also solves globally any CSP where there exists
a variable such that any other variable is reachable from it through a sequence
of functional constraints. Our experiments on random problems show that
variable elimination can significantly improve the efficiency of solving
problems with functional constraints
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