The photon absorption edge in superconductors and gapped 1D systems

Opening of a gap in the low-energy excitations spectrum affects the power-law singularity in the photon absorption spectrum $A(\Omega)$. In the normal state, the singularity, $A(\Omega)\propto [D/(\Omega-\Omega_{\rm th})]^\alpha$, is characterized by an interaction-dependent exponent $\alpha$. On the contrary, in the supeconducting state the divergence, $A(\Omega)\propto (D/\Delta)^\alpha(\Omega-\tilde{\Omega}_{\rm th})^{-1/2}$, is interaction-independent, while threshold is shifted, $\tilde{\Omega}_{\rm th}=\Omega_{\rm th}+\Delta$; the ``normal-metal'' form of $A(\Omega)$ resumes at $(\Omega-\tilde{\Omega}_{\rm th})\gtrsim \Delta\exp(1/\alpha)$. If the core hole is magnetic, it creates in-gap states; these states transform drastically the absorption edge. In addition, processes of scattering off the magnetic core hole involving spin-flip give rise to inelastic absorption with one or several {\it real} excited pairs in the final state, yielding a structure of peaks in $A(\Omega)$ at multiples of $2\Delta$ above the threshold frequency. The above conclusions apply to a broad class of systems, e.g., Mott insulators, where a gap opens at the Fermi level due to the interactions.Comment: 6 pages, 5 figures; published versio

The redox transformations and nucleophilic replacements as possible metabolic reactions of the drug “Triazaverin”. The chemical modeling of the metabolic processes

As a model of metabolic transformations of antiviral drug “Triazaverin” and its analogues‑2-alkylthio‑6-nitro‑1,2,4-triazolo[5,1-c][1,2,4]triazine‑7-ones 1a-d examined the oxidation of alkylthio groups to the corresponding sulfoxides 2a-d and sulfones 3a-d, as well as the process of nucleophilic substitution sulfonyloxy group of cysteine and cysteamine with the formation of compounds 5 and 6

Diazatriphenylenes and their thiophene analogues: Synthesis and applications

This review highlights the recent advances in the field of the synthesis of diazatriphenylenes and their structural analogues, such as phenanthrenes, fused with the thiophene ring, and naphthalenes, condensed with two thiophene rings. Also applications of these compounds are considered. © ARKAT USA, Inc.The research was financially supported by the Russian Science Foundation (Project No. 16-13-10435) and the Russian Foundation for Basic Research (research project №. 17-03-00011-А)

Iron based superconductors: magnetism, superconductivity and electronic structure

Angle resolved photoemission spectroscopy (ARPES) reveals the features of the electronic structure of quasi-two-dimensional crystals, which are crucial for the formation of spin and charge ordering and determine the mechanisms of electron-electron interaction, including the superconducting pairing. The newly discovered iron based superconductors (FeSC) promise interesting physics that stems, on one hand, from a coexistence of superconductivity and magnetism and, on the other hand, from complex multi-band electronic structure. In this review I want to give a simple introduction to the FeSC physics, and to advocate an opinion that all the complexity of FeSC properties is encapsulated in their electronic structure. For many compounds, this structure was determined in numerous ARPES experiments and agrees reasonably well with the results of band structure calculations. Nevertheless, the existing small differences may help to understand the mechanisms of the magnetic ordering and superconducting pairing in FeSC.Comment: Invited Revie

Nonequilibrium transport via spin-induced sub-gap states in superconductor/quantum dot/normal metal cotunnel junctions

We study low-temperature transport through a Coulomb blockaded quantum dot (QD) contacted by a normal (N), and a superconducting (S) electrode. Within an effective cotunneling model the conduction electron self energy is calculated to leading order in the cotunneling amplitudes and subsequently resummed to obtain the nonequilibrium T-matrix, from which we obtain the nonlinear cotunneling conductance. For even occupied dots the system can be conceived as an effective S/N-cotunnel junction with subgap transport mediated by Andreev reflections. The net spin of an odd occupied dot, however, leads to the formation of sub-gap resonances inside the superconducting gap which gives rise to a characteristic peak-dip structure in the differential conductance, as observed in recent experiments.Comment: 13 pages, 13 figures (new version contains reformulations and corrections of typos etc

Interplay between exchange-split Dirac and Rashba-type surface states at the MnBi2Te4/BiTeI interface

Based on ab initio calculations, we study the electronic structure of the BiTeI/MnBi2Te4 heterostructure interface composed of the antiferromagnetic topological insulator MnBi2Te4 and the polar semiconductor trilayer BiTeI. We found a significant difference in the electronic properties of the different contacts between the substrate and overlayer. While the case of a Te-Te interface forms a natural expansion of the substrate, when the Dirac cone state locates mostly in the polar overlayer region and undergoes a slight exchange splitting, the Te-I contact is the source of a four-band state contributed by the substrate Dirac cone and Rashba-type state of the polar trilayer. Owing to magnetic proximity, the pair of Kramers degeneracies for this state is lifted, which produces a Hall response in the transport regime. We believe our findings provide new opportunities to construct novel spintronic devices

5-(Methylidene)barbituric acid as a new anchor unit for dye-sensitized solar cells (DSSC)

Novel dyes bearing a 5-(methylidene)barbituric acid moiety as a new acceptor/anchor fragment were obtained and exhibited remarkable photophysical properties, according to a preliminary assessment of their sensitization activity as elements for dye-sensitized solar cells. © ARKAT-USA, Inc

Cyclotrimerization of 3-R-1,2,4-triazin-5(4H)-ones with cyclic ketones

New heterocyclic tetracyclic systems were synthesized. Interaction between 3-R-1,2,4-triazin-5(4H)-ones and cyclic ketones under acidic conditions leads to the formation of zwitterion derivatives of 5,6,7,8,9,10,11,12-octahydro-[1,2,4] triazino[1,6- f ]phenanthridine and 1,2,3,6,7,8-hexahydro-bicyclopenta[b,d] pyrido[1,2- f ][1,2,4]triazine. © 2010 Verlag der Zeitschrift für Naturforschung, Tübingen

An improved protocol for the preparation of 5, 11-dialkyl-6, 12-di(hetero)aryl-5, 11-dihydroindolo[3, 2-b]carbazoles and synthesis of their new 2, 8-dicyano-/2, 8-bis(benzo[d]thiazol-2-yl)-substituted derivatives

A number of 5, 11-dialkyl-6, 12-di(hetero)aryl-5, 11-dyhydroindolo[3, 2-b]carbazoles has been synthesized by modified method based on HBr catalyzed condensation of (hetero)aromatic aldehydes with indole in MeCN solution affording 5, 6, 11, 12-tetrahydroindolo[3, 2-b]carbazoles, that have been aromatized with I2 in DMF solution for 1 h at reflux, followed by alkylation of 5, 11-dihydro compounds. New 2, 8-dicyano-(10 examples) as well as 2, 8-bis(benzo[d]thiazol-2-yl)-substituted (5 examples) derivatives of these 5, 11-dyhydroindolo[3, 2-b]carbazoles have been obtained through their initial C2, 8-formylation, followed by treatment of dialdehydes with excess of hydroxylamine and dehydration of the formed aldoximes with acetic anhydride or by interaction with excess of 2-aminothiophenol in DMSO solution, respectively. © 2018 Arkat. All rights reserved.This research study was supported financially by the Russian Science Foundation (Project No. 16-13-10435)

Nucleophilic Substitution of Nitro Group in Dihydroazole[5,1-c][1,2,4]triazines

This work was supported by the Russian Foundation for Basic Research, project # 19-33-90086