Charged two-dimensional magnetoexciton and two-mode squeezed vacuum states

A novel unitary transformation of the Hamiltonian that allows one to partially separate the center-of-mass motion for charged electron-hole systems in a magnetic field is presented. The two-mode squeezed oscillator states that appear at the intermediate stage of the transformation are used for constructing a trial wave function of a two-dimensional (2D) charged magnetoexciton.Comment: 9 pages, 1 figur

Charged mobile complexes in magnetic fields: A novel selection rule for magneto-optical transitions

The implications of magnetic translations for internal optical transitions of charged mobile electron-hole ($e$--$h$) complexes and ions in a uniform magnetic field $B$ are discussed. It is shown that transitions of such complexes are governed by a novel exact selection rule. Internal intraband transitions of two-dimensional (2D) charged excitons $X^-$ in strong magnetic fields are considered as an illustrative example.Comment: 4 pages, 2 figure

Мutants of inflorescence development in alfalfa (Medicago sativa L.)

Alfalfa (Medicago sativa L., Medicago varia Mart., Medicago falcata L.) is a perennial leguminous plant  well-known as the queen of forages  cultivated  all over the world. The general  biology and morphology of the plant  has been described in detail. The typical inflorescence of the plant is raceme. Due to the multistep inbreeding process  in this cross-pollinated species, different mutant forms have been  found  in inbred  progenies. They include long racemes, panicle-like racemes  (with fertile and sterile flowers), complicated branched racemes,  and fasciated  inflorescences. The fasciation trait was discovered first in long racemes  and then it was introduced into every mutant inflorescence type by hand  pollination. By means  of pair hybridization,  transitional  forms of some mutants were isolated and the new mutant forms combined two or three  mutant genes.  New gene  names  are proposed for new duplex  and triplex mutant types: lpfas, pi1lpfas, brilpfas. Medicago truncatula is a conventional model species for legume  genome research. M. truncatula and alfalfa share highly conserved nucleotide sequences and exhibit nearly perfect  synteny between the two genomes. The knowledge about inflorescence development in model M. truncatula plants adds to understanding the genetic nature of mutant inflorescence development in alfalfa; therefore, we compiled the information on the genetic regulation of inflorescence development in M. truncatula. The M. truncatula mutant mtpim has a complicated inflorescence structure resembling panicle-like inflorescence in alfalfa. Presently, it is known that the inflorescence architecture in M. truncatula is controlled by spatiotemporal expression  of MtTFL1, MtFULc, MtAP1, and SGL1 through reciprocal repression.  Some mutants isolated in M. truncatula resemble alfalfa mutants in phenotype. The mutant generated by retrotransposon insertion mutagenesis and named sgl1-1 has a cauliflower-like phenotype looking just like the cauliflower mutant in alfalfa. New data concerning genes regulating inflorescence development in model legumes approach us to understanding the phenomenon of inflorescence mutations in alfalfa. The information of inflorescence mutants in nonmodel crops may augment our knowledge of plant development and help crop improvement

Two-dimensional magnetoexcitons in the presence of spin-orbit coupling

We study theoretically the effect of spin-orbit coupling on quantum well excitons in a strong magnetic field. We show that, in the presence of an in-plane field component, the excitonic absorption spectrum develops a double-peak structure due to hybridization of bright and dark magnetoexcitons. If the Rashba and Dresselhaus spin-orbit constants are comparable, the magnitude of splitting can be tuned in a wide interval by varying the azimuthal angle of the in-plane field. We also show that the interplay between spin-orbit and Coulomb interactions leads to an anisotropy of exciton energy dispersion in the momentum plane. The results suggest a way for direct optical measurements of spin-orbit parameters.Comment: 9 pages, 6 figure

Internal transitions of quasi-2D charged magneto-excitons in the presence of purposely introduced weak lateral potential energy variations

Optically detected resonance spectroscopy has been used to investigate effects of weak random lateral potential energy fluctuations on internal transitions of charged magneto-excitons (trions) in quasi two-dimensional GaAs/AlGaAs quantum-well (QW) structures. Resonant changes in the ensemble photoluminescence induced by far-infrared radiation were studied as a function of magnetic field for samples having: 1) no growth interrupts (short range well-width fluctuations), and 2) intentional growth interrupts (long range monolayer well-width differences). Only bound-to-continuum internal transitions of the negatively charged trion are observed for samples of type 1. In contrast, a feature on the high field (low energy) side of electron cyclotron resonance is seen for samples of type 2 with well widths of 14.1 and 8.4 nm. This feature is attributed to a bound-to-bound transition of the spin-triplet with non-zero oscillator strength resulting from breaking of translational symmetry.Comment: 16 pages, 3 figures, submitted to Physical Review

Goldstone Mode Relaxation in a Quantum Hall Ferromagnet due to Hyperfine Interaction with Nuclei

Spin relaxation in quantum Hall ferromagnet regimes is studied. As the initial non-equilibrium state, a coherent deviation of the spin system from the ${\vec B}$ direction is considered and the breakdown of this Goldstone-mode state due to hyperfine coupling to nuclei is analyzed. The relaxation occurring non-exponentially with time is studied in terms of annihilation processes in the "Goldstone condensate" formed by "zero spin excitons". The relaxation rate is calculated analytically even if the initial deviation is not small. This relaxation channel competes with the relaxation mechanisms due to spin-orbit coupling, and at strong magnetic fields it becomes dominating.Comment: 8 page

Seed quality evaluation in the collection of Cyamopsis tetragonoloba after long-term storage under uncontrolled conditions

Background. Guar or clusterbean (Cyamopsis tetragonoloba (L.) Taub.) is an annual leguminous plant cultivated for feed, food and industrial purposes. Its seed endosperm is used to extract guar gum, so the guar genetic resources stored in the VIR collection are of strategic importance for the import substitution policy in Russia in the context of their prospective introduction into cultivation in the country’s southern areas. Most of the guar accessions had been preserved by VIR for 40 years or more, so the task was to assess their germination rates and restore their viability. In the process of screening, seed quality parameters of the accessions were examined and analyzed.Materials and methods. VIR’s collection of C. tetragonoloba, initiated by N. I. Vavilov, now contains 111 accessions. Percentage seed viability, germination energy and seed hardness were evaluated in the Long-Term Storage Laboratory for 50 accessions reproduced in 2018 and for 263 older reproductions of 89 guar accessions. In total, 313 seed samples reproduced across 18 different years were analyzed. Statistica 10 software was used to perform a single-factor analysis of variance and find out how germination energy, seed viability and seed hardness correlated with the age of seeds, mean monthly temperature and mean rainfall during the growing season.Results and discussion. After more than 40 years of storage, the guar accessions did not entirely lost their viability under laboratory and field conditions. Very high positive correlations were found for their percentage viability and germination energy with the mean monthly temperature in the year of reproduction. A weak positive correlation was observed between seed hardness and the year of reproduction. Correlations between seed viability and rainfall during the growing season were weak, with a weak negative correlation between seed hardness and rainfall. The viability level of 30-year-old seeds was 50%, so guar may be regarded as belonging to the group of macrobiotic plants

Bose-Einstein condensation of quasiparticles in graphene

The collective properties of different quasiparticles in various graphene based structures in high magnetic field have been studied. We predict Bose-Einstein condensation (BEC) and superfluidity of 2D spatially indirect magnetoexcitons in two-layer graphene. The superfluid density and the temperature of the Kosterlitz-Thouless phase transition are shown to be increasing functions of the excitonic density but decreasing functions of magnetic field and the interlayer separation. The instability of the ground state of the interacting 2D indirect magnetoexcitons in a slab of superlattice with alternating electron and hole graphene layers (GLs) is established. The stable system of indirect 2D magnetobiexcitons, consisting of pair of indirect excitons with opposite dipole moments, is considered in graphene superlattice. The superfluid density and the temperature of the Kosterlitz-Thouless phase transition for magnetobiexcitons in graphene superlattice are obtained. Besides, the BEC of excitonic polaritons in GL embedded in a semiconductor microcavity in high magnetic field is predicted. While superfluid phase in this magnetoexciton polariton system is absent due to vanishing of magnetoexciton-magnetoexciton interaction in a single layer in the limit of high magnetic field, the critical temperature of BEC formation is calculated. The essential property of magnetoexcitonic systems based on graphene (in contrast, e.g., to a quantum well) is stronger influence of magnetic field and weaker influence of disorder. Observation of the BEC and superfluidity of 2D quasiparticles in graphene in high magnetic field would be interesting confirmation of the phenomena we have described.Comment: 13 pages, 5 figure