5,019 research outputs found
On conformally flat circle bundles over surfaces
We study surface groups in , which is the group of Mobius
tranformations of , and also the group of isometries of . We
consider such so that its limit set is a quasi-circle
in , and so that the quotient is a
circle bundle over a surface. This circle bundle is said to be conformally
flat, and our main goal is to discover how twisted such bundle may be by
establishing a bound on its Euler number. By combinatorial approaches, we have
two soft bounds in this direction on certain types of nice structures. In this
article we also construct new examples, a "grafting" type path in the space of
surface group representations into : starting inside the
quasi-Fuschsian locus, going through non-discrete territory and back.Comment: 28 pages, 7 figures. Updated from Thesis version: more correct bound
of (3/2)n^2, updated exposition in section 3.
Commuting-projector Hamiltonians for chiral topological phases built from parafermions
We introduce a family of commuting-projector Hamiltonians whose degrees of
freedom involve parafermion zero modes residing in a parent
fractional-quantum-Hall fluid. The two simplest models in this family emerge
from dressing Ising-paramagnet and toric-code spin models with parafermions; we
study their edge properties, anyonic excitations, and ground-state degeneracy.
We show that the first model realizes a symmetry-enriched topological phase
(SET) for which spin-flip symmetry from the Ising paramagnet
permutes the anyons. Interestingly, the interface between this SET and the
parent quantum-Hall phase realizes symmetry-enforced parafermion
criticality with no fine-tuning required. The second model exhibits a
non-Abelian phase that is consistent with topological order,
and can be accessed by gauging the symmetry in the SET.
Employing Levin-Wen string-net models with -graded structure,
we generalize this picture to construct a large class of commuting-projector
models for SETs and non-Abelian topological orders exhibiting
the same relation. Our construction provides the first
commuting-projector-Hamiltonian realization of chiral bosonic non-Abelian
topological order.Comment: 29+18 pages, 25 figure
Formation of high-quality Ag-based ohmic contacts to p-type GaN
Low resistance and high reflectance ohmic contacts on p-type GaN were achieved using an Ag-based metallization scheme. Oxidation annealing was the key to achieve ohmic behavior of Ag-based contacts on p-type GaN. A low contact resistivity of similar to 5x10(-5) Omega cm(2) could be achieved from Me (=Ni, Ir, Pt, or Ru)/Ag (50/1200 angstrom) contacts after annealing at 500 degrees C for 1 min in O(2) ambient. Oxidation annealing promoted the out-diffusion of Ga atoms from the GaN layer, and Ga atoms dissolved in the in-diffused Ag layer with the formation of Ag-Ga solid solution, resulting in ohmic contact formation. Using Ru/Ni/Au (500/200/500 angstrom) overlayers on the Me/Ag contacts, the excessive incorporation of oxygen molecules into the contact interfacial region, and the out-diffusion and agglomeration of Ag, were effectively prevented during oxidation annealing. As a result, a high reflectance of 87.2% at the 460 nm wavelength and a smooth surface morphology could be obtained simultaneously. (C) 2008 The Electrochemical Society.open111618sciescopu
The Eco-School Project at the Daegu National University of Education
Asia Education Symposium 2006, Session 3: “Making the most of Resources of International Education”( Day Two; Sun., October 16
Spin force and intrinsic spin Hall effect in spintronics systems
We investigate the spin Hall effect (SHE) in a wide class of spin-orbit
coupling systems by using spin force picture. We derive the general relation
equation between spin force and spin current and show that the longitudinal
force component can induce a spin Hall current, from which we reproduce the
spin Hall conductivity obtained previously using Kubo's formula. This simple
spin force picture gives a clear and intuitive explanation for SHE
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