534 research outputs found
Single-energy amplitudes for pion photoproduction in the first resonance region
We consider multipole amplitudes for low-energy pion photoproduction,
constructed with minimal model dependence, at single energies. Comparisons with
fits to the full resonance region are made. Explanations are suggested for the
discrepancies and further experiments are motivated.Comment: 12 pages, 5 figure
Interaction driven phases in the honeycomb lattice from exact diagonalization
We investigate the fate of interaction driven phases in the half-filled
honeycomb lattice for finite systems via exact diagonalization with nearest and
next nearest neighbour interactions. We find evidence for a charge density wave
phase, a Kekul\'e bond order and a sublattice charge modulated phase in
agreement with previously reported mean-field phase diagrams. No clear sign of
an interaction driven Chern insulator phase (Haldane phase) is found despite
being predicted by the same mean-field analysis. We characterize these phases
by their ground state degeneracy and by calculating charge order and bond order
correlation functions.Comment: 7 pages, 6 figures, updated reference
Breit - Wigner parameters of nucleon resonance S11(1535)
The result of partial - wave analysis of angular distributions for the
process gamma+p -> eta +p at the energies upto 2 GeV are given. From the energy
dependence of the regression coefficient a0(W) the reliable estimates of Breit
- Wigner parameters of S11(1535) - resonance and energy dependence of real and
imagenery parts of electric dipol amplitude E0+ and its phase were obtainedComment: 12 pages, 11 figure
Topological insulating phases in mono and bilayer graphene
We analyze the influence of different quadratic interactions giving rise to
time reversal invariant topological insulating phases in mono and bilayer
graphene. We make use of the effective action formalism to determine the
dependence of the Chern Simons coefficient on the different interactions
Charge instabilities and topological phases in the extended Hubbard model on the honeycomb lattice with enlarged unit cell
We study spontaneous symmetry breaking in a system of spinless fermions in
the Honeycomb lattice paying special emphasis to the role of an enlarged unit
cell on time reversal symmetry broken phases. We use a tight binding model with
nearest neighbor hopping t and Hubbard interaction V1 and V2 and extract the
phase diagram as a function of electron density and interaction within a mean
field variational approach. The analysis completes the previous work done in
Phys. Rev. Lett. 107, 106402 (2011) where phases with non--trivial topological
properties were found with only a nearest neighbor interaction V1 in the
absence of charge decouplings. We see that the topological phases are
suppressed by the presence of metallic charge density fluctuations. The
addition of next to nearest neighbor interaction V2 restores the topological
non-trivial phases
Topological Fermi liquids from Coulomb interactions in the doped Honeycomb lattice
We get an anomalous Hall metallic state in the Honeycomb lattice with nearest
neighbors only arising as a spontaneously broken symmetry state from a local
nearest neighbor Coulomb interaction V . The key ingredient is to enlarge the
unit cell to host six atoms that permits Kekul\'e distortions and supports
self-consistent currents creating non trivial magnetic configurations with
total zero flux. We find within a variational mean field approach a metallic
phase with broken time reversal symmetry (T) very close in parameter space to a
Pomeranchuk instability. Within the T broken region the predominant
configuration is an anomalous Hall phase with non zero Hall conductivity, a
realization of a topological Fermi liquid. A T broken phase with zero Hall
conductivity is stable in a small region of the parameter space for lower
values of V
Novel effects of strains in graphene and other two dimensional materials
The analysis of the electronic properties of strained or lattice deformed
graphene combines ideas from classical condensed matter physics, soft matter,
and geometrical aspects of quantum field theory (QFT) in curved spaces. Recent
theoretical and experimental work shows the influence of strains in many
properties of graphene not considered before, such as electronic transport,
spin-orbit coupling, the formation of Moir\'e patterns, optics, ... There is
also significant evidence of anharmonic effects, which can modify the
structural properties of graphene. These phenomena are not restricted to
graphene, and they are being intensively studied in other two dimensional
materials, such as the metallic dichalcogenides. We review here recent
developments related to the role of strains in the structural and electronic
properties of graphene and other two dimensional compounds.Comment: 75 pages, 15 figures, review articl
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