37 research outputs found
Fractional Quantum Hall States in Graphene
We quantum mechanically analyze the fractional quantum Hall effect in
graphene. This will be done by building the corresponding states in terms of a
potential governing the interactions and discussing other issues. More
precisely, we consider a system of particles in the presence of an external
magnetic field and take into account of a specific interaction that captures
the basic features of the Laughlin series \nu={1\over 2l+1}. We show that how
its Laughlin potential can be generalized to deal with the composite fermions
in graphene. To give a concrete example, we consider the SU(N) wavefunctions
and give a realization of the composite fermion filling factor. All these
results will be obtained by generalizing the mapping between the
Pauli--Schr\"odinger and Dirac Hamiltonian's to the interacting particle case.
Meantime by making use of a gauge transformation, we establish a relation
between the free and interacting Dirac operators. This shows that the involved
interaction can actually be generated from a singular gauge transformation.Comment: 20 page
Composite Fermion Description of the Excitations of the Paired Pfaffian Fractional Quantum Hall State
We review the recently developed bi-partite composite fermion model, in the context of so-called Pfaffian incompressible quantum liquid with fractional and non-Abelian quasiparticle statistics, a promising model for describing the correlated many-electron ground state responsible for fractional quantum Hall effect at the Landau level filling factor ? = 5/2. We use the concept of composite fermion partitions to demonstrate the emergence of an essential ingredient of the non-Abelian braid statistics – the topological degeneracy of spatially indistinguishable configurations of multiple widely separated (non-interacting) quasiparticles
Dynamical Mass Generation of Composite Dirac Fermions and Fractional Quantum Hall Effects near Charge Neutrality in Graphene
We develop a composite Dirac fermion theory for the fractional quantum Hall
effects (QHE) near charge neutrality in graphene. We show that the interactions
between the composite Dirac fermions lead to dynamical mass generation through
exciton condensation. The four-fold spin-valley degeneracy is fully lifted due
to the mass generation and the exchange effects such that the odd-denominator
fractional QHE observed in the vicinity of charge neutrality can be understood
in terms of the integer QHE of the composite Dirac fermions. At the filling
factor , we show that the massive composite Dirac fermion liquid is
unstable against chiral p-wave pairing for weak Coulomb interactions and the
ground state is a paired nonabelian state described by the Moore-Read Pfaffian
in the long wavelength limit.Comment: Extended, published version, 9 pages, 3 figure
Evaluation of the total photoabsorption cross sections for actinides from photofission data and model calculations
We have calculated the fission probabilities for 237-Np, 233,235,238-U,
232-Th, and nat-Pb following the absorption of photons with energies from 68
MeV to 3.77 GeV using the RELDIS Monte-Carlo code. This code implements the
cascade-evaporation-fission model of intermediate-energy photonuclear
reactions. It includes multiparticle production in photoreactions on
intranuclear nucleons, pre-equilibrium emission, and the statistical decay of
excited residual nuclei via competition of evaporation, fission, and
multifragmentation processes. The calculations show that in the GeV energy
region the fission process is not solely responsible for the entire total
photoabsorption cross section, even for the actinides: ~55-70% for 232-Th,
\~70-80% for 238-U, and ~80-95% for 233-U, 235-U, and 237-Np. This is because
certain residual nuclei that are created by deep photospallation at GeV photon
energies have relatively low fission probabilities. Using the recent
experimental data on photofission cross sections for 237-Np and 233,235,238-U
from the Saskatchewan and Jefferson Laboratories and our calculated fission
probabilities, we infer the total photoabsorption cross sections for these four
nuclei. The resulting cross sections per nucleon agree in shape and in
magnitude with each other. However, disagreement in magnitude with
total-photoabsorption cross-section data from previous measurements for nuclei
from C to Pb calls into question the concept of a ``Universal Curve'' for the
photoabsorption cross section per nucleon for all nuclei.Comment: 39 pages including 11 figure
Highly deformed Ca configurations in Si + C
The possible occurrence of highly deformed configurations in the Ca
di-nuclear system formed in the Si + C reaction is investigated
by analyzing the spectra of emitted light charged particles. Both inclusive and
exclusive measurements of the heavy fragments (A 10) and their
associated light charged particles (protons and particles) have been
made at the IReS Strasbourg {\sc VIVITRON} Tandem facility at bombarding
energies of Si) = 112 MeV and 180 MeV by using the {\sc ICARE}
charged particle multidetector array. The energy spectra, velocity
distributions, and both in-plane and out-of-plane angular correlations of light
charged particles are compared to statistical-model calculations using a
consistent set of parameters with spin-dependent level densities. The analysis
suggests the onset of large nuclear deformation in Ca at high spin.Comment: 33 pages, 11 figure
Crystal and molecular structure of powerine: Methyl 10,17-dihydroxy-(16?,17?,20?)-yohimban-16-carboxylate
Composite-particle emmision in the reaction p+Au at 2.5 Gev
The emission of composite-particles is studied in the reaction p+Au at Ep=2.5 GeV, in addition to neutrons and protons. Most particle energy spectra feature an evaporation spectrum superimposed on an exponential high-energy, non-statistical component. Comparisons are first made with the predictions by a two-stage hybrid reaction model, where an intra-nuclear cascade (INC) simulation is followed by a statistical evaporation process.The high-energy proton component is identified as product of the fast pre-equilibrium INC, since it is rather well reproduced by the INCL2.0 intra-nuclear cascade calculations simulating the first reaction stage. The low-energy spectral components are well understood in terms of sequential particle evaporation from the hot nuclear target remnants of the fast INC. Evaporation is modeled using the statistical code GEMINI. Implementation of a simple coalescence model in the INC code can provide a reasonable description of the multiplicities of high-energy composite particles such as 2–3H and 3He. However, this is done at the expense of 1H which then fails to reproduce the experimental energy spectra