2,815 research outputs found
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
Commuting-projector Hamiltonians for two-dimensional topological insulators: Edge physics and many-body invariants
Inspired by a recently constructed commuting-projector Hamiltonian for a two-dimensional (2D) time-reversal-invariant topological superconductor [Z. Wang et al., Phys. Rev. B 98, 094502 (2018)], we introduce a commuting-projector model that describes an interacting yet exactly solvable 2D topological insulator. We explicitly show that both the gapped and gapless boundaries of our model are consistent with those of band-theoretic, weakly interacting topological insulators. Interestingly, on certain lattices our time-reversal-symmetric models also enjoy CP symmetry, leading to intuitive interpretations of the bulk invariant for a CP-symmetric topological insulator upon putting the system on a Klein bottle. We also briefly discuss how these many-body invariants may be able to characterize models with only time-reversal symmetry
Percolation properties of growing networks under an Achlioptas process
We study the percolation transition in growing networks under an Achlioptas
process (AP). At each time step, a node is added in the network and, with the
probability , a link is formed between two nodes chosen by an AP. We
find that there occurs the percolation transition with varying and the
critical point is determined from the power-law behavior
of order parameter and the crossing of the fourth-order cumulant at the
critical point, also confirmed by the movement of the peak positions of the
second largest cluster size to the . Using the finite-size scaling
analysis, we get and , which
implies and . The Fisher exponent
for the cluster size distribution is obtained and shown to
satisfy the hyperscaling relation.Comment: 4 pages, 5 figures, 1 table, journal submitte
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