Triplet superconductivity in quasi one-dimensional systems

We study a Hubbard hamiltonian, including a quite general nearest-neighbor interaction, parametrized by repulsion V, exchange interactions Jz, Jperp, bond-charge interaction X and hopping of pairs W. The case of correlated hopping, in which the hopping between nearest neighbors depends upon the occupation of the two sites involved, is also described by the model for sufficiently weak interactions. We study the model in one dimension with usual continuum-limit field theory techniques, and determine the phase diagram. For arbitrary filling, we find a very simple necessary condition for the existence of dominant triplet superconducting correlations at large distance in the spin SU(2) symmetric case: 4V+J<0. In the correlated hopping model, the three-body interaction should be negative for positive V. We also compare the predictions of this weak-coupling treatment with numerical exact results for the correlated-hopping model obtained by diagonalizing small chains, and using novel techniques to determine the opening of the spin gap.Comment: 8 pages, 3 figure

Angle-resolved photoemission in doped charge-transfer Mott insulators

A theory of angle-resolved photoemission (ARPES) in doped cuprates and other charge-transfer Mott insulators is developed taking into account the realistic (LDA+U) band structure, (bi)polaron formation due to the strong electron-phonon interaction, and a random field potential. In most of these materials the first band to be doped is the oxygen band inside the Mott-Hubbard gap. We derive the coherent part of the ARPES spectra with the oxygen hole spectral function calculated in the non-crossing (ladder) approximation and with the exact spectral function of a one-dimensional hole in a random potential. Some unusual features of ARPES including the polarisation dependence and spectral shape in YBa2Cu3O7 and YBa2Cu4O8 are described without any Fermi-surface, large or small. The theory is compatible with the doping dependence of kinetic and thermodynamic properties of cuprates as well as with the d-wave symmetry of the superconducting order parameter.Comment: 8 pages (RevTeX), 10 figures, submitted to Phys. Rev.

Lattice dynamics effects on small polaron properties

This study details the conditions under which strong-coupling perturbation theory can be applied to the molecular crystal model, a fundamental theoretical tool for analysis of the polaron properties. I show that lattice dimensionality and intermolecular forces play a key role in imposing constraints on the applicability of the perturbative approach. The polaron effective mass has been computed in different regimes ranging from the fully antiadiabatic to the fully adiabatic. The polaron masses become essentially dimension independent for sufficiently strong intermolecular coupling strengths and converge to much lower values than those tradition-ally obtained in small-polaron theory. I find evidence for a self-trapping transition in a moderately adiabatic regime at an electron-phonon coupling value of .3. Our results point to a substantial independence of the self-trapping event on dimensionality.Comment: 8 pages, 5 figure

Phase diagram of the Holstein polaron in one dimension

The behavior of the 1D Holstein polaron is described, with emphasis on lattice coarsening effects, by distinguishing between adiabatic and nonadiabatic contributions to the local correlations and dispersion properties. The original and unifying systematization of the crossovers between the different polaron behaviors, usually considered in the literature, is obtained in terms of quantum to classical, weak coupling to strong coupling, adiabatic to nonadiabatic, itinerant to self-trapped polarons and large to small polarons. It is argued that the relationship between various aspects of polaron states can be specified by five regimes: the weak-coupling regime, the regime of large adiabatic polarons, the regime of small adiabatic polarons, the regime of small nonadiabatic (Lang-Firsov) polarons, and the transitory regime of small pinned polarons for which the adiabatic and nonadiabatic contributions are inextricably mixed in the polaron dispersion properties. The crossovers between these five regimes are positioned in the parameter space of the Holstein Hamiltonian.Comment: 19 pages, 9 figure

Risk-Oriented Model of the Distribution of Buildings (Structures) by Categories of Risk of Causing Harm (Damage) as the Result of Fire to Substantiate the Frequency of Scheduled Inspections of the Buildings (Structures)

Normative legal acts of the Russian Federation establish that the criteria for assigning control objects to the categories of risk of causing harm should be formed based on the results of the assessment of the risk of causing harm. In the developed countries of the world, as a rule, the distribution of objects of control by risk categories and the substantiation of the frequency of their inspections are carried out depending either on the point risk assessment, or on the number and importance of the violations of mandatory fire safety requirements revealed during the inspection of the object of control. The purpose of this work is to substantiate the frequency of scheduled inspections of the objects of control by the state fire supervision bodies depending on whether the objects of protection belong to a particular category of risk of causing harm. As a criterion for assigning control objects to various categories of risk of causing harm, it is proposed to use the risk of causing harm (damage) as the result of fire in the buildings of various classes of functional fire hazard, which is understood as the product of the probability of fire occurrence, the probability of causing socio-economic harm (damage) as the result of fire and the value terms of socio-economic harm (damage). A mathematical model was developed to determine the risk of causing harm (damage) as the result of a fire in a building, and an assessment of its values for the buildings of various classes of functional fire hazard is given. Distribution of the buildings by categories of risk of causing harm (damage) was carried out depending on the calculated value of the risk of causing harm. It is shown that the distribution of control objects by risk categories significantly depends on the degree of detail in the fire record card of the characteristics of the building in which the fire occurred. The optimal terms for carrying out scheduled inspections of the objects of control are proposed depending on the category of risk to which they are assigned. Proposals are formulated concerning the improvement of the risk-oriented approach in the activities of the state fire supervision bodies of the EMERCOM of Russia.</jats:p