Hole-doped cuprates exhibit partially coexisting pseudogap (PG), charge ordering (CO) and superconductivity; we show that there exists a class of systems in which they have a single nature as it has ...recently been supposed. Since the charge-ordered phase exhibits large frozen deformation of the lattice, we develop a method for calculating the phase diagram of a system with strong long-range (Fröhlich) electron-phonon interaction. Using a variational approach, we calculate the free energy of a two-liquid system of carriers with cuprate-like dispersion comprising a liquid of autolocalized carriers (large polarons and bipolarons) and Fermi liquid of delocalized carriers. Comparing it with the free energy of pure Fermi liquid and calculating (with standard methods of Bose liquid theory) a temperature of the superfluid transition in the large-bipolaron liquid we identify regions in the phase diagram with the presence of PG (caused by the impact of the (bi)polarons potential on delocalized quasiparticles), CO and superconductivity. They are located in the same places in the diagram as in hole-doped cuprates, and, as in the latter, the shape of the calculated phase diagram is resistant to wide-range changes in the characteristics of the system. As in cuprates, the calculated temperature of the superconducting transition increases with the number of conducting planes in the unit cell, the superfluid density decreases with doping at overdoping, the bipolaron density (and bipolaronic plasmon energy) saturates at optimal doping. Thus, the similarity of the considered system with hole-doped cuprates is not limited to the phase diagram. The results obtained allow us to discuss ways of increasing the temperature of the superfluid transition in the large-bipolaron liquid and open up the possibility of studying the current-carrying state and properties of the bipolaron condensate.
We propose the principles of structural organization in spherical nanoassemblies with icosahedral symmetry constituted by asymmetric protein molecules. The approach modifies the paradigmatic ...geometrical Caspar and Klug (CK) model of icosahedral viral capsids and demonstrates the common origin of both the "anomalous" and conventional capsid structures. In contrast to all previous models of "anomalous" viral capsids the proposed modified model conserves the basic structural principles of the CK approach and reveals the common hidden symmetry underlying all small viral shells. We demonstrate the common genesis of the "anomalous" and conventional capsids and explain their structures in the same frame. The organization principles are derived from the group theory analysis of the positional order on the spherical surface. The relationship between the modified CK geometrical model and the theory of two-dimensional spherical crystallization is discussed. We also apply the proposed approach to complex double-shelled capsids and capsids with protruding knob-like proteins. The introduced notion of commensurability for the concentric nanoshells explains the peculiarities of their organization and helps to predict analogous, but yet undiscovered, double-shelled viral capsid nanostructures.
We propose the principles of structural organization in spherical nanoassemblies with icosahedral symmetry constituted by asymmetric protein molecules.
A model resulting in charge ordering (CO) similar to that observed in cuprate superconductors is under study. It includes strong long-range electron-phonon interaction (EPI) and high density of ...correlated carriers. Coexistence of large bipolarons and delocalized carriers is a feature of such system. We develop generalized variation method to calculate the bipolaron size (CO period) in the ground normal state of such system at various doping. The approach allows the revealing of a possible physical reason of strongly different doping behavior of the CO wave vector in different cuprates. Obtained doping dependences of the CO period and temperature of the CO decay demonstrate quantitative agreement with those observed in cuprates. Predicted in the suggested approach ratio of the CO wave vector to the wave vector of the high-energy anomaly (HEA) in ARPES spectrum is in consent with that in cuprates. Calculated resonant x-rays scattering on the CO emerging in the model is in good agreement with experiments on cuprates including the asymmetry of the CO peaks' cross-section. A gap arises in the spectrum of delocalized carriers near antinodal direction due to their scattering on the periodic potential created by autolocalized carriers, analogously to photon crystal effect.
An approach to considering systems with a high concentration of correlated carriers and strong long-range electron-phonon interaction and to calculating the high-energy part of the angle-resolved ...photoemission spectroscopy (ARPES) spectra of such systems is suggested. Joint relaxation of strongly coupled fields-a field of correlated electrons and phonon field-after photoemission is studied to clarify the nature of characteristic features observed in the high-energy part of the ARPES spectra of cuprate superconductors. Such relaxation occurs in systems with strong predominantly long-range electron-phonon interaction at sufficiently high carrier concentration due to the coexistence of autolocalized and delocalized carriers. A simple method to calculate analytically a high-energy part of the ARPES spectrum arising is proposed. It takes advantage of using the coherent states basis for the phonon field in the polaron and bipolaron states. The approach suggested yields all the high-energy spectral features like broad Gaussian band and regions of 'vertical dispersion' being in good quantitative agreement with the experiments on cuprates at any doping with both types of carriers. Demonstrated coexistence of autolocalized and delocalized carriers in superconducting cuprates changes the idea about their ground state above the superconducting transition temperature that is important for understanding transport and magnetic properties. High density of large-radius autolocalized carriers revealed may be a key to the explanation of charge ordering in doped cuprates.
To advance Thomson problem we generalize physical principles suggested by Caspar and Klug (CK) to model icosahedral capsids. Proposed simplest distortions of the CK spherical arrangements yield ...new-type trial structures very close to the lowest energy ones. In the region 600≤N≤1000, where N is the number of particles in the structure, we found 40 new spherical crystals with the lowest ever seen energies and curvature-induced topological defects being not the well-known elongated scars but flatten pentagons. These crystals have N values prohibited in the CK model and demonstrate a new way to combine the local hexagonal order and spherical geometry.
•We break the icosahedral symmetry of Caspar and Klug model of viral capsids.•Simplest distortion of global icosahedral arrangement in 2D nanocrystals is found.•Trial 2D spherical structures obtained are close to the lowest energy Thomson ones.•A new way to combine the local hexagonal order and spherical geometry is proposed.•List of Thomson structures with the lowest seen energies is essentially updated.
Extended topological defects (ETDs) arising in spherical hexagonal crystals due to their curvature are considered. These prevalent defects carry a unit total topological charge and are surrounded by ...scalene pentagonal boundaries. Topological peculiarities of reactions between ETDs and dislocations are considered. Similarly to boundaries of the usual planar crystalline order the ETDs emit and absorb the dislocations without preservation of their dislocational charge. Dislocations located inside the ETD area lose it and the enforced ETD decay can proceed in different ways without conservation of the total Burgers vector of the dislocations emitted.
•Reactions between defects in spherical order can change their total Burgers vector.•Extended topological defect is formed by a disclination and a set of vacancies.•Dislocations inside the topological defect area lose initial dislocation charges.•Shift of the extended topological defect emits or absorbs the dislocations.
Real-time signal compression-recovery based on the Prony method is examined and the complexity and time consuming nature of the calculations are demonstrated. An approach to the compression and ...recovery of signals based on a combination of the Prony method and an expansion in sign-varying components is described.
Strong electron–phonon interaction (EPI) generating spontaneous breaking translational symmetry (polarons formation) is acknowledged in lightly doped cuprates due to interpretation of broad bands in ...their ARPES and optical conductivity spectra. To study systems with strong EPI at significant carrier density we construct distribution suitable for carriers with momentum uncertainty. Obtained concentrations of carriers in different states are used to predict ARPES spectra of such systems. Doping evolution of spectra calculated and “vertical dispersion” in them demonstrate the excellent qualitative and quantitative agreement with those observed in cuprates. “Vertical dispersion” in undoped and essentially doped cuprates is understood from a single viewpoint.
•Strong Frohlich electron–phonon coupling at essential carriers density is studied.•Carriers distribution admitting states with momentum uncertainty is constructed.•It describes the momentum space partition between autolocalized and free carriers.•Filled autolocalized states kill the low-momentum part of free-carriers dispersion.•This displays itself in ARPES spectra as “waterfalls” observed in cuprates.
Pseudogap in hole-doped cuprate superconductors is acknowledged as a possible key to understanding their ground normal state, however, existing pseudogap models have essential inconsistencies with ...experiments. In our approach pseudogap emerges due to impact of autolocalized carriers on stationary states of delocalized ones and topology of the 2D hole-like dispersion. Autolocalized carriers create potential which transforms Bloch quasiparticles into distributed wave packets (DWPs) with different momentums in areas with different potential. Topology of hole-like constant energy curves in 2D-conducting cuprates forbids DWPs with average momentums near antinode. Manifestation of permitted DWPs in ARPES spectra demonstrates all known pseudogap features including midpoint shift, giant broadening and Fermi momentum misalignment. Calculated doping dependence of the pseudogap width and onset temperature agrees with experiments. The obtained ground normal state of the hole-doped cuprates, in which all the doped holes are autolocalized until high doping is reached and near-antinodal electron DWPs are absent, explains Fermi surface reconstruction from small electron pocket to large hole-like Fermi surface observed in quantum oscillation measurements. Our results open a possibility of creating systems with artificial pseudogap and switchable density of states on the base of highly polarizable layered structures with 2D conductivity and hole-like dispersion.
•Quasiparticles in potential of autolocalized carriers are distributed wave packets.•Topology of hole-like constant-energy curves bans new quasiparticles near antinode.•Display of permitted quasiparticles in ARPES and STM spectra demonstrates pseudogap.•Doping dependence of pseudogap width and onset temperature agrees with experiments.•Obtained ground normal state explains Fermi surface reconstruction in cuprates.
The objective of this study was to develop a mathematical model and conduct a computer simulation of the transient thermal state of a composite coating, and to determine the penetration depth during ...laser remelting on a metal substrate to obtain a high-entropy alloy coating. A simplified mathematical model was formulated, representing a boundary value problem for calculating the transient thermal state of a composite coating. A computer program has been developed, which made it possible to determine the penetration depth of the coating layer, made of a mixture of powders of five different metals, to estimate the shrinkage of the molten coating at different levels of laser power, spot diameter, and scanning rate over the surface of the treated material. The developed program also enables establishing the position dynamics of two-dimensional boundary lines of the two-phase region for the liquidus and solidus of a given metal or alloy included in the mixture. The developed model can be adapted for practical use based on the experimental data on coating porosity and thickness before and after melting of simple systems with similar thermophysical properties. As an example, the calculation of the process of transient heating of a system of metal powders of nickel, iron, cobalt, chromium, and copper in equal mass fractions was considered.
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