First Principle Electronic Model for High-Temperature Superconductivity

Using the structural data of the La2CuO4 compound both in the low temperature tetragonal phase and in the isotropic phase we have derived an effective t-J model with hoppings t and superexchange interactions J extended up to fourth and second neareast neighbors respectively. By numerically studying this hamiltonian we have then reproduced the main experimental features of this HTc compound: d-wave superconductivity is stabilized at small but finite doping delta>6% away from the antiferromagnetic region and some evidence of dynamical stripes is found at commensurate filling 1/8.Comment: 4 pages including 4 figures and 2 table

Electronic structure of FeSe monolayer superconductors

We review a variety of theoretical and experimental results concerning electronic band structure of superconducting materials based on FeSe monolayers. Three type of systems are analyzed: intercalated FeSe systems A_xFe_2Se_{2-x}S_x and [Li_{1-x}Fe_xOH]FeSe as well as the single FeSe layer films on SrTiO_3 substrate. We present the results of detailed first principle electronic band structure calculations for these systems together with comparison with some experimental ARPES data. The electronic structure of these systems is rather different from that of typical FeAs superconductors, which is quite significant for possible microscopic mechanism of superconductivity. This is reflected in the absence of hole pockets of the Fermi surface at \Gamma-point in Brillouin zone, so that there are no "nesting" properties of different Fermi surface pockets. LDA+DMFT calculations show that correlation effects on Fe-3d states in the single FeSe layer are not that strong as in most of FeAs systems. As a result, at present there is no theoretical understanding of the formation of rather "shallow" electronic bands at M points. LDA calculations show that the main difference in electronic structure of FeSe monolayer on SrTiO_3 substrate from isolated FeSe layer is the presence of the band of O-2p surface states of TiO_2 layer on the Fermi level together with Fe-3d states, which may be important for understanding the enhanced T_c values in this system. We briefly discuss the implications of our results for microscopic models of superconductivity.Comment: 21 pages, 13 figures, minor typos correcte

Optical orientation and alignment of excitons in direct and indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment

The spin structure and spin dynamics of excitons in an ensemble of (In,Al)As/AlAs quantum dots (QDs) with type-I band alignment, containing both direct and indirect band gap dots, are studied. Time-resolved and spectral selective techniques are used to distinguish between the direct and indirect QDs. The exciton fine structure is studied by means of optical alignment and optical orientation techniques in magnetic fields applied in the Faraday or Voigt geometries. A drastic difference in emission polarization is found for the excitons in the direct QDs involving a $\Gamma$-valley electron and the excitons in the indirect QDs contributed by an $X$-valley electron. We show that in the direct QDs the exciton spin dynamics is controlled by the anisotropic exchange splitting, while in the indirect QDs it is determined by the hyperfine interaction with nuclear field fluctuations. The anisotropic exchange splitting is determined for the direct QD excitons and compared with model calculations

Optical orientation and alignment of excitons in direct and indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment

The spin structure and spin dynamics of excitons in an ensemble of (In,Al)As/AlAs quantum dots (QDs) with type-I band alignment, containing both direct and indirect band gap dots, are studied. Time-resolved and spectral selective techniques are used to distinguish between the direct and indirect QDs. The exciton fine structure is studied by means of optical alignment and optical orientation techniques in magnetic fields applied in the Faraday or Voigt geometries. A drastic difference in emission polarization is found for the excitons in the direct QDs involving a $\Gamma$-valley electron and the excitons in the indirect QDs contributed by an $X$-valley electron. We show that in the direct QDs the exciton spin dynamics is controlled by the anisotropic exchange splitting, while in the indirect QDs it is determined by the hyperfine interaction with nuclear field fluctuations. The anisotropic exchange splitting is determined for the direct QD excitons and compared with model calculations

On Microscopic Origin of Integrability in Seiberg-Witten Theory

We discuss microscopic origin of integrability in Seiberg-Witten theory, following mostly the results of hep-th/0612019, as well as present their certain extension and consider several explicit examples. In particular, we discuss in more detail the theory with the only switched on higher perturbation in the ultraviolet, where extra explicit formulas are obtained using bosonization and elliptic uniformization of the spectral curve.Comment: 24 pages, 1 figure, LaTeX, based on the talks at 'Geometry and Integrability in Mathematical Physics', Moscow, May 2006; 'Quarks-2006', Repino, May 2006; Twente conference on Lie groups, December 2006 and 'Classical and Quantum Integrable Models', Dubna, January 200

Editorial: CRISPR-Cas in Agriculture: Opportunities and Challenges

CRISPR-Cas genome editing technology is developing at a rapid pace and new molecular tools, such as CRISPR nucleases, are becoming regularly available. As part of this Research Topic, Bandyopadhyay et al. provide a comprehensive overview of Cas12a, a CRISPR nuclease formerly known as Cpf1. In their review article, the authors cover structural and mechanistic aspects of Cas12a in comparison with Cas9, the most commonly used CRISPR nuclease. They also highlight uses of Cas12a for the purpose of improving agriculturally important traits in various crops. An overview of Cas9 genome editing applications in plants is provided by El-Mounadi et al. who introduce the reader to the mechanism of Cas9 activity, methods of its delivery to plant cells (i.e., transformation techniques), give examples of improving crop traits using CRISPR-Cas9, and touch on biosafety and regulatory aspects associated with genome editing. A number of countries (e.g., the USA, Brazil, Argentina, and Japan) have already exempted genome edited crops, which do not carry transgenic DNA or novel combination of genetic material (i.e., not similarly achievable through conventional breeding), from being regulated similarly to Genetically Modified Organisms (GMOs) as genetically engineered (GE) organisms (Schmidt et al., 2020). Although the above-mentioned countries have passed legislation allowing cultivation of genome edited crops without GE regulation, the public dialogue and policy developments on the issue are evolving. In the case of Japan, Tabei et al. analyse Twitter conversation on genome-edited foods and their labelling over the period from May to October 2019. The analysis reveals that 54.5% of relevant tweets were statements opposed to food produced using genome edited crops, while only 7% were statements in favour of it. The remaining 38.5% of tweets were statements deemed neutral. Although the analysis was not necessarily representative of the wider Japanese society due to bias among Twitter users, the study underlines the importance of a continuous public dialogue on the issue of genome edited crops in Japan and the rest of the world