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I. M. Yurin

Publications and source records attributed to I. M. Yurin.

11 recordsLinked to original sources
arXiv2015

The He II Theory Preserving the Symmetry of the Initial Hamiltonian of the System

The article suggests a method for the construction of the number of atoms preserving microscopic He II theory. The suggested theory can provide the ground state wave function (WF) as an expansion in series by small parameters. In addition, errors in the definition of the WFs of the excited states turn out to be vanishingly small while the system size increases. Predictions of the proposed theory and of the Bogoliubov theory are identical if helium occupies a simply connected volume. However, there are differences in the general case. These differences are due to the fact that the operator of the occupation number of the zero momentum state does not commute with the creation and annihilation operators of phonons. This contradicts the Bogoliubov assumption that the creation and annihilation operators of atoms in the zero momentum state can be replaced by a c-number. The latter, as is known, should commute with any operator. This should lead to a difference in the results of calculation of helium flow through the tunnel transition. Therefore, the suggested theory is not equivalent to Bogoliubov theory.

cond-mat.supr-con↗
arXiv2009

Coexistence of the "bogolons" and the one-particle spectrum of excitations with a gap in the degenerated Bose gas

Properties of the weakly non-ideal Bose gas are considered without suggestion on C-number representation of the creation and annihilation operators with zero momentum. The "density-density" correlation function and the one-particle Green function of the degenerated Bose gas are calculated on the basis of the self-consistent Hartree-Fock approximation. It is shown that the spectrum of the one-particle excitations possesses a gap whose value is connected with the density of particles in the "condensate". At the same time, the pole in the "density-density" Green function determines the phonon-roton spectrum of excitations which exactly coincides with one discovered by Bogolyubov for the collective excitations (the "bogolons").

cond-mat.quant-gas↗
arXiv2009

The Possibility of Existence of an Energy Gap in the One-Particle Excitation Spectrum of He II

Possibility for coexistence of a phonon and one-particle spectra in ${}^4He$ at all temperatures including temperatures below the $λ$ - point is shown. An approach developed to consider the problem of the weakly imperfect Bose gas results in the existence of a gap in the one-particle (one-atom) excitation spectrum below the transition point. Thus, the microscopic model of He II turns out to differ both from the model initially suggested by Landau and from the Bogolyubov model accepted at present. Analysis of the experimental data obtained by measuring enthalpy and the part of helium atoms condensed in the state with the momentum $p=0$ enabled to estimate the size of the gap. It turned out to be approximately equal to 0.31 K at zero temperature.

cond-mat.supr-con↗
arXiv2008

Comparison of Two Interpretations of Josephson Effect

This paper puts forward an interpretation of the Josephson effect based on the Alternative Theory of Superconductivity (ATS). A comparison of ATS- and BCS-based interpretations is provided. It is demonstrated that the ATS-based interpretation, unlike that based on BCS theory, does not require a revision of fundamentals of quantum physics.

physics.gen-ph↗
arXiv2006

Calculation of the Superconductivity Gap of Metal from Its Parameters in Normal State

A previously considered model interpreted a superconductor as an electron gas immersed in a medium with the dielectric constant $ε$ and a certain elasticity, which could be determined by measured sonic speed in the metal. The obtained expression of effective electron-electron interaction (EEI) potential unambiguously implied that, contrary to the suggestions of BCS theory, it is its long-wave limit which is responsible for the emergence of bound two-electron states and, consequently, for gap formation in one-electron spectrum of the metal. However, the existence of singularities in the EEI potential expression continued to pose a problem, which did not allow a calculation of the gap value for specific superconducting materials, first of all, for metals belonging to periodic table (PT). In the present work, I suggest taking into account matrix elements traditionally attributed to electron scattering in EEI effective potential calculations. For superconductors that has been made on the basis of a semiconductor material by implanting electro-active defects into it, this inclusion results in the appearance of an uncertainty of electron momentum $δp \sim l^{- 1}$, where $l$ is the electron free path. When considering pure PT metals, Hamiltonian terms relating to creation and annihilaton of phonons should be taken into account, which also produces an uncertainty of electron momentum. This uncertainty results in a regularization of EEI potential expression and, therefore, in a possibility of examination of physical properties of specific superconductors. Results of calculation of superconductivity gap value for a range of simple metals (Al, Zn, Pb, Sn) confirm the consistency of the developed approach.

cond-mat.supr-con↗
arXiv2003

Superconductivity in the Model with non Cooper Pairs

On a basis of earlier substantiated expression for effective potential of electron-electron attraction in metals the assumption of an opportunity of formation of classically bound pairs is put forward. It was shown that in distinction from the Cooper pair, the energy of the electron pair in this approach is negative in the centrum of mass of the pair. This fact changes the pattern of the superconductivity phenomenon in the proposed model. First, the gap in the one-particle spectrum appears due to the effect of a "mean field" on the energy of electron state from the side of occupied states, the nearest neighbors over the momenta grid. Second, the condensate is formed by electron states with energies below that of the gap edge. No Bose condensation does occur in the system proceeding from the proposed model. In quasi-classical approximation Londons' hypothesis is substantiated.

cond-mat.supr-con↗
arXiv2002

New approach to the superconductivity problem

In this work, a question is tackled concerning the formation of a superconducting condensate in an earlier proposed model of "elastic jelly", in which phonons of the ion system play the part of initiating ones. It was shown that in distinction from the BCS theory, the momenta of forming electron pairs are different from zero. This fact changes the pattern of the description of the superconductivity phenomenon in the proposed model. First, the gap in the one-electron spectrum appears due to the effect of a "mean field" on the energy of electron state from the side of occupied states, the nearest neighbors over the momenta grid. Second, the condensate is formed by electron states with energies below that of the gap edge, this is why the Fermi-condensation arises in the system. Third, anomalous expectation values are strictly equal to zero in the proposed model.

cond-mat.supr-con↗
arXiv2001

Superconductivity in the Model of Elastic Jelly

In this work, a question is tackled concerning the formation of a superconducting condensate in an earlier proposed model of "elastic jelly", in which phonons of the valent skeleton play the part of initiating ones. It was shown that in distinction from the BCS theory, the momenta of forming electron couples are different from zero. This fact changes the pattern of the description of the superconductivity phenomenon in the proposed model. First, the gap in the one-electron spectrum appears due to the effect of a "mean field" on the energy of one-electron state from the side of occupied states, the nearest neighbors over the momenta grid. Second, the condensate is formed by one-electron states with energies below that of the gap edge. This is why the Fermi-condensation arises in the system. Third, in the proposed theory the electron couples appear in the form of low-energy excitations, i.e., as those with the minimum amount of energy per excitation electron. Hence, their role is minimized to that of low-energy excitation with the minimum energy per electron, and they are no more "bricks" the superconducting condensate is made of, as the case is in the BCS theory.

cond-mat.supr-con↗
arXiv2001

The Condition for the Onset of High Temperature Superconductivity

In this work the long-wave limit of electron-electron interaction arising from the exchange of virtual phonons in an approximation close to "jelly" model is considered. It is shown that the interaction through the exchange of virtual phonons is actually not screened in contrast to the Coulomb one; this just leads to instability relative to the formation of pairs near the Fermi surface. The consequences of this approach are examined with respect to high-temperature superconducting materials that have recently been synthesized. An approximate relationship connecting sound and Fermi velocities for these materials is obtained.

cond-mat.supr-con↗