399 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
Tunable Casimir repulsion with three dimensional topological insulators
In this Letter, we show that switching between repulsive and attractive
Casimir forces by means of external tunable parameters could be realized with
two topological insulator plates. We find two regimes where a repulsive
(attractive) force is found at small (large) distances between the plates,
canceling out at a critical distance. For a frequency range where the effective
electromagnetic action is valid, this distance appears at length scales
corresponding to .Comment: 9 pages, 5 figures, published version with auxiliary material.
Featured in Physical Review Focu
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
Linear and nonlinear optical responses in the chiral multifold semimetal RhSi
Chiral topological semimetals are materials that break both inversion and
mirror symmetries. They host interesting phenomena such as the quantized
circular photogalvanic effect (CPGE) and the chiral magnetic effect. In this
work, we report a comprehensive theoretical and experimental analysis of the
linear and non-linear optical responses of the chiral topological semimetal
RhSi, which is known to host multifold fermions. We show that the
characteristic features of the optical conductivity, which display two distinct
quasi-linear regimes above and below 0.4 eV, can be linked to excitations of
different kinds of multifold fermions. The characteristic features of the CPGE,
which displays a sign change at 0.4 eV and a large non-quantized response peak
of around 160 at 0.7 eV, are explained by assuming that
the chemical potential crosses a flat hole band at the Brillouin zone center.
Our theory predicts that, in order to observe a quantized CPGE in RhSi, it is
necessary to increase the chemical potential as well as the quasiparticle
lifetime. More broadly our methodology, especially the development of the
broadband terahertz emission spectroscopy, could be widely applied to study
photo-galvanic effects in noncentrosymmetric materials and in topological
insulators in a contact-less way and accelerate the technological development
of efficient infrared detectors based on topological semimetals.Comment: Accepted in npj Quantum Materials; Abstract update
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
Second-harmonic generation in the topological multifold semimetal RhSi
Recent experiments in the topological Weyl semimetal TaAs have observed record-breaking second-harmonic generation (SHG), a nonlinear optical response at 2? generated by an incoming light source at ?. However, whether SHG is enhanced in topological semimetals in general is a challenging open question because their band structure entangles the contributions arising from trivial bands and topological band crossings. In this work, we circumvent this problem by studying RhSi, a chiral topological semimetal with a simple band structure with topological multifold fermions close to the Fermi energy. We measure SHG in a wide frequency window, ? [0.27,1.5]eV and, using first-principles calculations, we establish that, due to their linear dispersion, the contribution of multifold fermions to SHG is subdominant as compared with other regions in the Brillouin zone. Our calculations suggest that parts of the bands where the dispersion is relatively flat contribute significantly to SHG. As a whole, our results suggest avenues to enhance SHG responses. © 2022 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society
Ambiguities in the partial-wave analysis of pseudoscalar-meson photoproduction
Ambiguities in pseudoscalar-meson photoproduction, arising from incomplete
experimental data, have analogs in pion-nucleon scattering. Amplitude
ambiguities have important implications for the problems of amplitude
extraction and resonance identification in partial-wave analysis. The effect of
these ambiguities on observables is described. We compare our results with
those found in earlier studies.Comment: 12 pages of text. No figure
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
Effect of finite temperature and uniaxial anisotropy on the Casimir effect with three-dimensional topological insulators
In this work we study the Casimir effect with three-dimensional topological
insulators including the effects of temperature and uniaxial anisotropy.
Although precise experimental values for the optical properties of these
materials are yet to be established, qualitative analysis is still possible. We
find qualitatively that the reported repulsive behavior and the equilibrium
point are robust features of the system, and are favored by low temperatures
and the enhancement of the optical response parallel to the optical axis. The
dependence of the equilibrium point with temperature and with the topological
magnetoelectric polarizability characteristic of three-dimensional topological
insulators is also discussed.Comment: 17 pages, 7 figures. Published versio
- …