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The magnetic and electronic structures of Fe4O5 have been investigated at ambient and high pressures via a combination of representation analysis, density functional theory (DFT+U) calculations, and M\"ossbauer spectroscopy. A few spin configurations corresponding to the different irreducible representations have been considered. The total-energy calculations reveal that the magnetic ground state of Fe4O5 corresponds to an orthogonal spin order. Depending on the magnetic propagation vector k two spin ordered phases with minimal energy differences are realized. The lowest energy magnetic phase is related to k = (0, 0, 0) and is characterized by the ferromagnetic ordering of the iron magnetic moments at prismatic sites along the b axis and antiferromagnetic ordering of iron moments at octahedral sites along the c axis. For the k = (1/2, 0, 0) phase, the moments in the prisms are antiferromagnetically ordered along the b axis and the moments in the octahedra are still antiferromagnetically ordered along the c axis. Under high pressure, the Fe4O5 exhibits magnetic transitions with corresponding electronic transitions of the metal-insulator type. At a critical pressure PC ~ 60 GPa the Fe ions at the octahedral sites undergo a high-spin to low-spin state crossover with a decrease in the unit-cell volume of ~ 4%, while the Fe ions at the prismatic sites remain in the high-spin state up to 130 GPa. This site-dependent magnetic collapse is experimentally observed in the transformation of M\"ossbauer spectra measured at room temperature and high pressures., Comment: 25 pages, 11 figurs, 5 tables

Physics of high-$T_c$ superconducting cuprates is obscured by the effect of strong electronic correlations. One way to overcome the problem is to seek for an exact solution at least within the small cluster and expand it to the whole crystal. Such an approach is in the heart of the cluster perturbation theory (CPT). Here we develop CPT for the dynamic spin and charge susceptibilities (spin-CPT and charge-CPT), within which the correlation effects are explicitly taken into account by the exact diagonalization. We apply spin-CPT and charge-CPT to the effective two-band Hubbard model for the cuprates obtained from the three-band Emery model and calculate one- and two-particle correlation functions, namely, spectral function and spin and charge susceptibilities. Doping dependence of the spin susceptibility was studied within spin-CPT and CPT-RPA that is the CPT generalization of the random phase approximation (RPA). Both methods produce the low energy response at four incommensurate wave vectors in qualitative agreement to the results of the inelastic neutron scattering on overdoped cuprates., Comment: 14 pages, 8 figures

Ultrafast quantum dynamics relaxation of a photoexcited state in a strongly correlated spin crossover system LaCoO3 under a sudden perturbation is considered with the density matrix generalized master equation. The magnetization and cobalt-oxygen bond length oscillations were found. The evolution of the electronic band structure during relaxation is calculated in the framework of the LDA+GTB method.

SummaryHijacking the cellular protein degradation system offers unique opportunities for drug discovery, as exemplified by proteolysis targeting chimeras (PROTACs). Despite their superior properties over classical inhibitors, it has so far not been possible to reprogram the bacterial degradation machinery to interfere with microbial infections. Here, we develop small-molecule degraders, so-called BacPROTACs, that bind to the substrate receptor of the ClpC:ClpP protease, priming neo-substrates for degradation. In addition to their targeting function, BacPROTACs activate ClpC, transforming the resting unfoldase into its functional state. The induced higher-order oligomer was visualized by cryo-EM analysis, providing a structural snapshot of activated ClpC unfolding a protein substrate. Finally, degradation assays performed in mycobacteria demonstrate in vivo activity of BacPROTACs, highlighting the potential of the technology to provide next generation antibiotics.

The microscopic origin of ultrafast modification of the ratio between the symmetric (J) and antisymmetric (D) exchange interaction in antiferromagnetic iron oxides is revealed, using femtosecond laser excitation as a pump and terahertz emission spectroscopy as a probe. By tuning the photon energy of the laser pump pulse we show that the effect of light on the D/J ratio in two archetypical iron oxides FeBO3 and ErFeO3 is maximized when the photon energy is in resonance with a spin and parity forbidden d-d transition between the crystal-field split states of Fe3+ ions. The experimental findings are supported by a multielectron model, which accounts for the resonant absorption of photons by Fe3+ ions. Our results reveal the importance of the parity and spin-change forbidden, and therefore often underestimated, d-d transitions in ultrafast optical control of magnetism.

Within the multielectron model of magnetic insulator with spin crossover under high pressure we have studied the mean field phase diagrams in pressure temperature plane and dynamics of a sudden excited non equilibrium spin state. We obtain the different relaxation of the magnetization, high spin/low spin occupation numbers, and the metal oxygen bond length for different values of the external pressure. We found the long living oscillations of magnetization without pressure and at small external pressure. Close to crossover pressure the smooth relaxation is accompanied with a set of sharp strongly non linear oscillations of magnetization and HS/LS occupation numbers that are accompanied by the Franck Condon resonances.

The values and signs of the contributions to the superexchange interaction of Co3+ ions in LaCoO3 in different spin states, namely, the superexchange of a pair of ions in the intermediate (IS) state and the superexchange of a pair of ions, one of which is in the intermediate state and the other in the high-spin (HS) state, are studied. For this purpose, virtual electron-hole pairs produced in the course of superexchange (the so-called exchange loops) have been studied within the framework of a multiband generalization of the Hubbard model. It is shown that the cobalt ions in the intermediate state are ordered ferromagnetically, while a pair of ions in different HS and IS states makes an AFM contribution to the superexchange. Keywords: superexchange interaction, magnetic structure, Hubbard model, projection operator method, exchange loop.

© 2018 The Author(s). Every two years groups worldwide participate in the Critical Assessment of Protein Structure Prediction (CASP) experiment to blindly test the strengths and weaknesses of their computational methods. CASP has significantly advanced the field but many hurdles still remain, which may require new ideas and collaborations. In 2012 a web-based effort called WeFold, was initiated to promote collaboration within the CASP community and attract researchers from other fields to contribute new ideas to CASP. Members of the WeFold coopetition (cooperation and competition) participated in CASP as individual teams, but also shared components of their methods to create hybrid pipelines and actively contributed to this effort. We assert that the scale and diversity of integrative prediction pipelines could not have been achieved by any individual lab or even by any collaboration among a few partners. The models contributed by the participating groups and generated by the pipelines are publicly available at the WeFold website providing a wealth of data that remains to be tapped. Here, we analyze the results of the 2014 and 2016 pipelines showing improvements according to the CASP assessment as well as areas that require further adjustments and research.

The work was supported by the Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Region Science and Technology Support Fund project no. 18-42-243022. This work is partially supported by the Ministry of Education and Science of the Russian Federation and by Siberian Branch of the Russian Academy of Sciences (Project II.8.70) and Fundamental research program of the Presidium of the RAS no. 32 «Nanostructures: physics, chemistry, biology, basics of technologies». This work was supported by and carried out on the equipment of the Center for Common Use of the Krasnoyarsk Scientific Center, Siberian Branch, Russian Academy of Sciences.

In this work we investigate doping and temperature dependences of electronic structure of system with strong electronic correlations and strong electron-phonon interaction modeling cuprates in the frameworks of the three-band p-d-Holstein model by a polaronic version of the generalized tight binding (GTB) method. Within this approach the electronic structure is formed by polaronic quasiparticles constructed as excitations between initial and final polaronic multielectron states. Doping and temperature effects are taken into account by occupation numbers of local excited polaronic states and variations in the magnitude of spin-spin correlation functions. Both effects are manifested in the reconstruction of band structure, Fermi contours, density of states and redistribution of the spectral weight over the Hubbard polaron subbands. Doping leads to transformation of Fermi contour from small hole pockets around k=(pi/2,pi/2) with inhomogeneous spectral weight distribution at small hole concentration to large contour around k=(pi,pi) in the overdoped compound as a result of two quantum phase transitions. In the system with phonon subsystem and EPI doping results in the top of the valence band splitting off and new polaron subbands appearance. Temperature increasing in the system with doped holes and moderate EPI leads to formation of the flatband around k=(pi,pi) and transfer of the spectral weight to the splitted off top of the valence band., 10 pages, 6 figures, 22 references. arXiv admin note: substantial text overlap with arXiv:1611.05836

We suggest here the method of the mapping of DFT calculations on the multiorbital model in a following way: the parameters of the formulated multiorbital model should be determined from the requirement that the self-consistent charge and spin densities found from the ab initio and model calculations have to be as close to each other as possible. The analysis of the model allows for detailed understanding of the role played by different parameters of the model in the physics of interest. As an example of the approach we present the study of the effect of silicon atoms substitution by the iron atoms and vice versa on the magnetic properties in the iron silicide alpha-FeSi2. The DFT+GGA calculations are mapped to the model with intraatomic Coulomb and exchange interactions, hoppings to nearest and next nearest atoms and exchange of the delocalized electrons between iron atoms; the magnetic moments on atoms and charge densities of the material are found self-consistently within the Hartree-Fock approximation. We find that while the stoichiometric alpha-FeSi2 is nonmagnetic, the substitutions generate different magnetic structures. For example, the substitution of three Si atoms by the Fe atoms results in the ferrimagnetic structure whereas the substitution of four Si atoms by Fe atoms gives rise to either the nonmagnetic or the ferromagnetic state depending on the type of local enviroment of the substitutional Fe atoms. Besides, contrary to the commonly accepted statement that the destruction of the magnetic moment is controlled only by the number of Fe-Si nearest neighbors, we find that actually it is controlled by the Fe-Fe next-nearest-neighbors. This finding led us to the counterintuitive conclusion: an increase of Si concentration in Fe1-xSi2+x ordered alloys may lead to a ferromagnetism. This conclusion is confirmed by the calculation within GGA-to-DFT.

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Single-crystalline MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4 have been grown by the flux method. The samples have been characterized by X-ray spectral analysis, X-ray diffraction, and X-ray absorption spectroscopy. The X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra have been measured at the Fe and Co K-edges over a wide temperature range (6.5–300 K). The composition, the charge state, and local environment of both Fe and Co atoms have been determined. The effects of Co substitution for Mg on the local structural distortions have been revealed experimentally and the M-O bond anisotropy has been found., This work has been financed by the MECOM Project MAT11/23791, and DGA IMANA project E-34, Council for Grants of the President of the Russian Federation (project nos. NSh-2886.2014.2, SP-938.2015.5), and Russian Foundation for Basic Research (project nos. 13-02-00958-a, 13-02-00358-a, 14-02-31051-mol-a).

The ferromagnetic Fe-In2O3 nanocomposite thin film has been synthesized by the thermite Fe2O3 + In → Fe-In2O3 reaction. The transmittance (400 – 1100 nm) was measured at temperatures from 320 to 5 K. It was found that the transmittance increases when temperature decreases. For wavelength 600, 700, 800, 900 and 1000 nm maximum change of transmittance was ~ 3.2, 4.2, 4.8, 5.1 and 5.4 %, respectively. From transmittance spectra, spin glass-like behavior was observed near ~ 36 K and confirmed by magnetization measurements. The Verwey transition was identified at ~ 127 K by magnetization measurements. We have shown direct relationship between transmittance and magnetization of nanocomposite Fe – In2O3 thin film near ~ 36 K and give proposed possible mechanism this phenomena.

In many cases the standard perturbation approach appears to be too simple to describe precisely the angle resolved photoemission spectrum of strongly correlated electron system. In particular, to describe the momentum asymmetry observed in photoemission spectra of high-Tc cuprates a phenomenological approach based on extremely correlated Fermi-liquid model has been recently introduced. In this paper we analyze the general structure of the Green function of quasiparticles in strongly correlated electron systems and stress that it is defined not only by the self-energy of Hubbard quasiparticles but also by a strength operator. We show that the later leads to an additional odd momentum contribution to the spectral function and alone can explain the observed asymmetry. So, the asymmetry of the ARPES spectra can be a measure of the strength of electron correlations in materials., 4 pages

Single crystalline MgFeBO_4, Mg_0.5Co_0.5FeBO_4 and CoFeBO_4 have been grown by the flux method. The samples have been characterized by X-ray spectral analysis, X-ray diffraction and X-ray absorption spectroscopy. The X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra have been measured at the Fe andCoK-edges over a wide temperature range (6.5 - 300 K). The composition, the charge state and local environment of both Fe and Co atoms have been determined. The effects of Mg substitution by Co on the local structural distortions have been revealed experimentally and the M-O bond anisotropy has been found., Comment: 21 pages, 11 figures, 4 tables

We present ab initio results for the electron-phonon interaction of the \Gamma-point phonons in the tetragonal high-temperature phase of La2CuO4. Eigenfrequencies and eigenvectors for the symmetry-allowed phonon modes are calculated with the full-potential augmented plane wave+local orbitals method using the frozen phonon approach. It is found that the \Gamma-point phonons with the strongest electron-phonon interaction are the A{2u} modes with 236 cm^{-1}, 131 cm^{-1} and 476 cm^{-1}. To take effect of strong electron on-site interaction into account we use generalized tight-binding method that results in the interaction of phonons with Hubbard fermions forming quasiparticle's band structure. Finally, the matrix elements of Hubbard fermion-phonon interaction and their reduction due to strong electron correlation are obtained., Comment: 7 pages

Resumen del trabajo presentado al "V Euro-Asian Symposium Trends in MAGnetism: Nanomagnetism" celebrado en Vladivostok (Rusia) del 15 al 21 de septiembre de 2013., The field of research on nanostructures of ferromagnetic metal/semiconductormaterials is subject of interest due to their unique physical properties for applications in microelectronics, spintronics, etc. In this work we focus our research on the particular case of (Fe/Si)n multilayer magnetic structures with an odd number of Fe layers and their interfaces. The interlayer exchange coupling (IEC) between two ferromagnetic layers across a nonmagnetic spacer leads to applications in mass storage, nonvolatile memory and sensors. However, the presence of nonmagneticsilicides decreases the current spin polarization in the silicon spacerlayer and affects the mechanism of IEC. It is, therefore, of utmost importanceto control the interlayer composition. Samples are prepared by sequential deposition of Fe/Sibilayers in molecular beam epitaxy (MBE) set-ups in ultrahigh vacuum and at room temperature. Two different substrates have been used: a Si(100) wafer with a thin SiO2 buffer layer (type A) and an in situ prepared buffer layer of Ag(100) on Fe/GaAs(100) (type B). To characterize the morphology and chemical constitution of the films and their interfaces, high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS), angle-resolved x-ray photoelectron spectroscopy (ARXPS), high energy x-ray photoelectron spectroscopy (HAXPES), x-ray reflectivity (XRR), and conversion electron Mössbauer spectroscopy (CEMS) have been used. The magnetic properties were obtained from SQUID magnetometry and magneto-optic (MOKE) imaging of the magnetic domain structures. From the comprehensive analysis of all data we conclude that the as-deposited A and B samples show non-magnetic Fe silicide formation at the nominal Si spacers. As temperature is increased, at about 400 K, the A samples undergo diffusion of Si into the Fe films, reacting to form even more non-magnetic silicide. In contrast, in the B samples, the chemical reaction implies the transformation of non-magnetic silicides formed during deposition into ferromagnetic Fe3Si in a first step, and into non-magnetic silicides like ε-FeSi in a second step. The difference is attributed to the substrate, which in the case A is capable of supplying through the thin SiO2 buffer all Si needed to undergo the transition to ε-FeSi, while in the case B this cannot occur since the substrate contains no Si. The interface constitution, roughness, and asymmetry in the deposition are reviewed.

The article considers the key aspects of creation of the new global information society problem, connected with modes of mass supervision in information-communication networks.

The article considers a particular activity, carried out by the SSSEU in the light of solution of complex economic-social managerial problems, and forthcoming entry of the Russian Federation to the World Trade Organization, that demands for the appropriate personnel provision, capable to increase efficiency of managerial activity in business-structures due to prospective decisions on the basis of capacities of modern information technologies.

Ferropericlase, (Mg,Fe)O is one of the most abundant minerals of the Earth's lower mantle. The high-spin (HS) to low-spin (LS) transition in the Fe2+ ions can dramatically alter the physical and chemical properties of (Mg,Fe)O in the deep mantle, thereby changing our understanding of the Earth's deep interior. To establish a fundamental understanding of the ground electronic state of iron, the electronic and magnetic states of Fe2+ in (Mg0.75,Fe0.25)O have been investigated by transmission (TMS) and synchrotron (NFS) M\"ossbauer spectroscopy at high pressures and low temperatures (down to 5 K). The results show that the ground electronic state of Fe2+ at the critical pressure Pc of the spin transition and close to T=0 is determined by a quantum critical point Pq (T = 0, Pc) where the energy difference between the HS and LS states (an energy gap for the spin fluctuation) is zero. The deviation from T=0 leads to the thermal excitation for the HS or LS state, suggesting a strong influence on the magnetic and hence the physical properties of the material. Combining these with theoretical calculations, the results indicate that the existence of the quantum critical point at zero temperature affects not only the low-temperature physical properties, but also the strong temperature/pressure-dependent properties at conditions relevant to the middle layer of the lower mantle.

For many years a spin-state transition at $T \approx 100 K$ and insulator - metal transition (IMT) at $T_{IMT} \approx 600 K$ in LaCoO$_3 $ remains a mystery. Small low-spin - high-spin spin gap $\Delta _S = E\left( {HS} \right) - E\left( {LS} \right) \sim 100 K$ results in the spin-state transition. The large charge gap $2E_a \approx 2300 K$ ($E_a $ is the activation energy) vs. $\Delta _S $ and $T_{IMT} $ implies that LaCoO$_3 $ is not a simple narrow-gap semiconductor. Here we explain both the spin-state and IMT on the same footing. We obtain strong temperature dependent band structure in LaCoO$_3 $ by the LDA+GTB method that incorporates strong electron correlations, covalence and spin-orbital interaction exactly inside the CoO$_6 $ cluster and the interclaster hopping between different multielectron configurations by perturbation theory for Hubbard X-operators.

Complex cobalt oxides known as cobaltites are reviewed, including LnCoO3-based perovskite-structured rare-earth cobaltites (where Ln is lanthanum or a lanthanide), quasi-two-dimensional and quasi-one-dimensional cobaltites of the types LnCo2O5+δ, La 2CoO4, and Ca3Co2O8, and NaxCoO2 yH2O superconducting compounds. Key experimental and theoretical results are presented, with emphasis on the interplay between charge, spin, and orbital degrees of freedom. Two problems of specific relevance to cobaltites - the spin state instability of Co3+ ions in LnCoO3, and the nature of superconductivity in Na xCoO2 yH2O - are also given significant attention. © 2009 Uspekhi Fizicheskikh Russian Academy of Sciences.

We study the doping evolution of the electronic structure in the normal phase of high-$T_c$ cuprates. Electronic structure and Fermi surface of cuprates with single CuO$_2$ layer in the unit cell like La$_{2-x}$Sr$_x$CuO$_4$ have been calculated by the LDA+GTB method in the regime of strong electron correlations (SEC) and compared to ARPES and quantum oscillations data. We have found two critical concentrations, $x_{c1}$ and $x_{c2}$, where the Fermi surface topology changes. Following I.M. Lifshitz ideas of the quantum phase transitions (QPT) of the 2.5-order we discuss the concentration dependence of the low temperature thermodynamics. The behavior of the electronic specific heat $\delta(C/T) \sim (x - x_c)^{1/2}$ is similar to the Loram and Cooper experimental data in the vicinity of $x_{c1} \approx 0.15$., Comment: 8 pages, 4 figures

Strong electron correlations are responsible both for the insulator ground state of undoped La$_2$CuO$_4$ and strong antiferromagnetic coupling $J$ between neighbouring spins. We consider magnetic mechanism of superconducting pairing in the effective low energy $t - t' - t" - J^*$ model with all parameters calculated {\it ab initio}. Interaction of strongly correlated electrons with different phonon modes is also incorporated. In a BCS type theory the $d_{x^2 - y^2}$ gap is given by a sum of magnetic and phonon contributions. The phonon coupling parameter $\lambda = f(x)G$, where $G$ is a combination of bare electron-phonon couplings for all modes and the function $f$ depends on the hole concentration $x$ due to strong electron correlations. The main contribution to the only fitting parameter $G$ is determined by a competition of the breathing and buckling modes. Fitting the parameter $G$ from the isotope effect we obtain that magnetic and phonon contributions to the critical temperature $T_c $ work together and are of the same order of magnitude., Comment: 10 pages, 5 figures

The t-t'-t''-J model of electrons interacting with three phonon modes (breathing, apical breathing, and buckling) is considered. The wave-vector dependence of the matrix elements of the electron-phonon interaction leads to opposite contributions to the pairing potential with the d-symmetry: the buckling mode facilitates electron pairing, while the breathing mode suppresses it. As a result, the critical temperature of La{2 - x}Sr{x}CuO{4} that is associated with the magnetic mechanism is lowered when phonons are taken into account., 5 pages, 3 figures

Any medium can be represented as an isometric subgraph of the hypercube, with each token of the medium represented by a particular equivalence class of arcs of the subgraph. Such a representation, although useful, is not especially revealing of the structure of a particular medium. We propose an axiomatic definition of the concept of a `mediatic graph'. We prove that the graph of any medium is a mediatic graph. We also show that, for any non-necessarily finite set S, there exists a bijection from the collection M of all the media on a given set S (of states) onto the collection G of all the mediatic graphs on S., Four axioms replaced by two; two references added; Fig.6 corrected

Media theory is a new branch of discrete applied mathematics originally developed in mid-nineties to deal with stochastic evolution of preference relations in political science and mathematical psychology. However, many different examples of media can be found, ranging from learning spaces to hypercube computers, suggesting that this concept is ubiquitous. The paper presents very basic concepts and results of media theory and is aimed at a wide body of researchers in discrete applied mathematics.

We review the normal and superconducting state properties of the unconventional triplet superconductor Sr2RuO4 with an emphasis on the analysis of the magnetic susceptibility and the role played by strong electronic correlations. In particular, we show that the magnetic activity arises from the itinerant electrons in the Ru d-orbitals and a strong magnetic anisotropy occurs (χ+- < χzz) due to spin-orbit coupling. The latter results mainly from different values of the g-factor for the transverse and longitudinal components of the spin susceptibility (i.e. the matrix elements differ). Most importantly, this anisotropy and the presence of incommensurate antiferromagnetic and ferromagnetic fluctuations have strong consequences for the symmetry of the superconducting order parameter. In particular, reviewing spin fluctuation-induced Cooper-pairing scenario in application to Sr 2RuO4 we show how p-wave Cooper-pairing with line nodes between neighboring RuO2-planes may occur. We also discuss the open issues in Sr2RuO4 like the influence of magnetic and non-magnetic impurities on the superconducting and normal state of Sr 2RuO4. It is clear that the physics of triplet superconductivity in Sr2RuO4 is still far from being understood completely and remains to be analyzed more in more detail. It is of interest to apply the theory also to superconductivity in heavy-fermion systems exhibiting spin fluctuations. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In the framework of the effective low-energy model for High-$T_c$ cuprates with account for three-centers interaction terms and spin fluctuations the properties of normal and superconducting phases of p- and n-type cuprates are investigated. Microscopic model parameters were obtained from ARPES data on undoped compounds. Obtained evolution of the chemical potential with doping, Fermi Surface at optimal doping, and $T_c(x)$ phase diagram for n-type cuprates are in remarkably good agreement with the experiment. It is shown that the spin-exciton mechanism due to singlet-triplet hybridization takes place in p-type, although it is too small to reproduce observed qualitative difference between p- and n-type cuprates., Comment: 10 pages, 3 figures, IOP LaTeX

We review the normal and superconducting state properties of the unconventional triplet superconductor Sr2RuO4 with an emphasis on the analysis of the magnetic susceptibility and the role played by strong electronic correlations. In particular, we show that the magnetic activity arises from the itinerant electrons in the Ru d-orbitals and a strong magnetic anisotropy occurs (χ+- < χzz) due to spin-orbit coupling. The latter results mainly from different values of the g-factor for the transverse and longitudinal components of the spin susceptibility (i.e. the matrix elements differ). Most importantly, this anisotropy and the presence of incommensurate antiferromagnetic and ferromagnetic fluctuations have strong consequences for the symmetry of the superconducting order parameter. In particular, reviewing spin fluctuation-induced Cooper-pairing scenario in application to Sr 2RuO4 we show how p-wave Cooper-pairing with line nodes between neighboring RuO2-planes may occur. We also discuss the open issues in Sr2RuO4 like the influence of magnetic and non-magnetic impurities on the superconducting and normal state of Sr 2RuO4. It is clear that the physics of triplet superconductivity in Sr2RuO4 is still far from being understood completely and remains to be analyzed more in more detail. It is of interest to apply the theory also to superconductivity in heavy-fermion systems exhibiting spin fluctuations. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We have analyzed the quasiparticle dispersion and ARPES-spectral density for Sr2CuO2Cl2 and Ca2CuO2Cl2 antiferromagnetic insulators along basic symmetric directions of the Brillouin zone (BZ) in a framework of an extended tight binding method (ETBM) with explicit account for intracell strong electron correlations. The quasiparticle dispersion is in a good agreement with ARPES- data. At the top of valence band we found a narrow impurity-like virtual level with the spectral weight proportional to the concentration of spin fluctuations. A pseudogap between the virtual level and the top of the valence band has dispersion similar to 'remnant Fermi surface' in Ca2CuO2Cl2 and to a pseudogap in the underdoped Bi2212 samples. A calculated parity of the polarized ARPES-spectra in (0,0),(pi/2,pi/2),(pi,0) - points in the AFM- phase is even with regard to relative magnitudes of the partial contributions by different orbitals to the total ARPES- spectral density. Conditions of an observability for the different partial contributions in the polarized ARPES- experiments are determined also., Comment: 15 pdf-pages with 10 figures and table

We show, following W. Holsztynski, that there exists a continuous metric d on the set of real numbers R such that any finite metric space is isometrically embeddable into (R,d)., Comment: 3 pages

To compare the superconductivity in strongly correlated electron systems with the antiferromagnetic fluctuations in the copper oxides and with the ferromagnetic fluctuations in Sr_2RuO_4 a t-J-I model is proposed. The antiferromagnetic coupling J results in the superconducting state of d_{x^2-y^2} symmetry and the ferromagnetic coupling constant I results in the spin-triplet p-type state. The difference in the gap anisotropies provides the large difference in T_c values, for the typical values of the coupling constants: T_c of order of 1K for the ruthenate and T_c of order of 100K for the cuprates., 4 pages, RevTEX, 3 figs. Submitted to Phys. Rev. Lett