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

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

Cytogenetic factors decreasing the fertility of pollen and cobs during clogging of tetraploid maize with triploid grains (<i>Zea mays</i> L.)

Background. Clogging of tetraploid maize crops with triploid grains leads to a decrease in grain yield and the destruction of the genome’s stability. Searching for the reasons of the tetraploid genome’s decomposition as well as solving the problem of seed yield reduction in freely pollinated crops of tetraploid maize remains relevant.Materials and methods. Cultivars of tetraploid dentate (k-23427) and sweet (k-23426) maize from VIR and dentate (k-24735) and sweet maize (k-23425) hybrids served as the material of the research. The experiments were carried out in the foothill zone of Kabardino-Balkaria. Incubation and hybridization were carried out under parchment insulators. Metaphase plates of maize roots were stained with Schiff’s reagent according to Feulgen and pollen grains were stained with Lugol’s solution.Results. Triploid grains, along with diploid ones, were able to germinate and show poor fertility. As a result of the fusion between male gametes of triploid and female tetraploid plants, an imbalance in the stability of the tetraploid genome occurred, leading to increased degradation of the cultivar’s productivity with each seed reproduction. A cytological analysis and the results of test crosses ♀2n × ♂3n, ♀4n × ♂3n showed that in self-pollinated triploid plants the frequency of diploid kernel formation was 7.44%; triploid + aneuploidy, 41.78%; tetraploid, 50.74%; and in test crosses the frequency of diploid ones was 18.22%; triploid + aneuploid, 63.83%; and tetraploid, 36.15%. The analysis of segregation classes with the determination of Pearson’s χ2  criterion showed that instead of the expected segregation 1(2n) : 7(3n) + (Xn±1x) : 1(4n), diploid, triploid + aneuploid and tetraploid kernels developed on self-pollinated triploid plants in the ratio of 2 : 13 : 16, respectively, and in test crosses for the 2n and 4n genotypes splitting into diploid, triploid + aneuploid, and tetraploid grains occurred in the ratio of 7 : 18 : 14, respectively

Exceedingly facile Ph−X activation (X=Cl, Br, I) with ruthenium(II) : Arresting kinetics, autocatalysis, and mechanisms

The ICIQ Foundation and The Spanish Government (Grant CTQ2011-25418 and the Severo Ochoa Excellence Accreditation 2014-2018 SEV-2013-0319) are thankfully acknowledged for support of this work. F.M.M. is grateful to the Government of Spain (MICINN) for the FPI Ph.D. Scholarship (BES-2012-054922). S.A.M. and D.M. thank the EPSRC for support through award EP/J010677/1.[(Ph3P)3Ru(L)(H)2] (where L=H2 (1) in the presence of styrene, Ph3P (3), and N2 (4)) cleave the Ph[BOND]X bond (X=Cl, Br, I) at RT to give [(Ph3P)3RuH(X)] (2) and PhH. A combined experimental and DFT study points to [(Ph3P)3Ru(H)2] as the reactive species generated upon spontaneous loss of L from 3 and 4. The reaction of 3 with excess PhI displays striking kinetics which initially appears zeroth order in Ru. However mechanistic studies reveal that this is due to autocatalysis comprising two factors: 1) complex 2, originating from the initial PhI activation with 3, is roughly as reactive toward PhI as 3 itself; and 2) the Ph[BOND]I bond cleavage with the just-produced 2 gives rise to [(Ph3P)2RuI2], which quickly comproportionates with the still-present 3 to recover 2. Both the initial and onward activation reactions involve PPh3 dissociation, PhI coordination to Ru through I, rearrangement to a η2-PhI intermediate, and Ph[BOND]I oxidative addition.Publisher PDFPeer reviewe