A translation invariant bipolaron in the Holstein model and superconductivity

Large-radius translation invariant (TI) bipolarons are considered in a one-dimensional Holstein molecular chain. Criteria of their stability are obtained. The energy of a translation invariant bipolaron is shown to be lower than that of a bipolaron with broken symmetry. The results obtained are applied to the problem of superconductivity in 1D-systems. It is shown that TI-bipolaron mechanism of Bose-Einstein condensation can support superconductivity even for infinite chain.Comment: 20 pages, 7 figures. This version contains essentially new results in comparison with v1. The Abstract is enlarged, the Introduction is improved. Four sections are added. This version was published in SpringerPlus (2016) 5:1277, here Table 1 is correcte

Large-radius Holstein polaron and the problem of spontaneous symmetry breaking

A translation-invariant solution is found for a large-radius Holstein polaron whose energy in the strong coupling limit is lower than that obtained by Holstein. The wave function corresponding to this solution is delocalized. A conclusion is made about the absence of a spontaneous symmetry breaking in the quantum system discussed.Comment: 20 pages, 4 figures. Appendix A and references 24, 25, 26 were added. Progress of Theoretical and Experimental Physics, accepte

Translation Invariant Bipolaron Theory of Superconductivity and Spectroscopic Experiments

The explanation of the nature of superconducting gap in high temperature superconductors (HTSC) is a fundamental task which solution can lead to the understanding of superconducting mechanism. However, it has not been fully solved yet. From the mid of the twentieth century when Bardeen, Cooper and Schrieffer constructed their theory it has been believed that a superconducting gap is a collective phenomenon of electron excitations. In this work it is demonstrated that according to translation-invariant bipolaron theory of HTSC the different types of experiments measure for the gap different values. Thus tunneling experiments determine the bipolaron energy for a superconducting gap. On the other hand, the angle - resolved photoemission spectroscopy method measures the phonon frequency for which the electron-phonon interaction is maximum. Such effects as kinks in spectral measurements of gap, its angular dependence, existence of pseudogap and others have got natural explanations.Comment: Title changed, references added. Enhanced and improved version. 12 pages, 8 figure

Superconducting properties of a nonideal bipolaron gas

The properties of a Bose gas of translation-invariant (TI) bipolarons analogous to Cooper pairs are considered. As in the BCS theory, the description of a TI-bipolaron gas is based on the electron-phonon interaction and Froehlich Hamiltonian. As distinct from the BCS theory, when the correlation length greatly exceeds the mean distance between the pairs, here we deal with the opposite case when the correlation length is much less than the distance between the pairs. We calculate the critical temperature of the transition of a TI-bipolaron Bose-gas into the superconducting state, its energy, heat capacity and heat of the transition. The results obtained are used to explain the experiments on high-temperature superconductors. Possible ways of raising the critical temperature of high-temperature superconductors are discussed.Comment: 27 pages, 5 figure

Pekar's Ansatz and the Strong Coupling Problem in Polaron Theory

A detailed consideration is given to the translation-invariant theory of Tulub polaron constructed without the use of Pekar ansatz. A fundamental result of the theory is that the value of the polaron energy is lower than that obtained on the basis of Pekar ansatz which was considered as an asymptotically exact solution in the strong coupling limit. In the case of bipolarons the theory yields the best values of the coupling energy and critical parameters of their stability. Numerous physical consequences of the existence of translation-invariant polarons and bipolarons are discussed.Comment: 35 pages, 4 figures. Physics-Uspekhi (Advances in Physical Sciences), 2015, accepted. Draft versio

Translation invariant theory of polaron (bipolaron) and the problem of quantizing near the classical solution

A physical interpretation of translation-invariant polarons and bipolarons is presented, some results of their existence are discussed. Consideration is given to the problem of quantization in the vicinity of the classical solution in the quantum field theory. The lowest variational estimate is obtained for the bipolaron energy E(\eta) with E(0)=-0,440636\alpha^2, where \alpha is a constant of electron-phonon coupling, \eta is a parameter of ion binding

On the term of the 4-th order with respect to the field operators in the translation-invariant polaron theory

It is shown that 4-th order term in the translation-invariant polaron theory vanishes.Comment: 3 page

Davydov's Solitons in a Homogeneous Nucleotide Chain

Charge transfer in homogeneous nucleotide chains is modeled on the basis of Holstein Hamiltonian. The path length of Davydov solitons in these chains is being studied. It is shown that in a dispersionless case, when the soliton velocity V is small, the path length grows exponentially as V decreases. In this case the state of a moving soliton is quasisteady. In the presence of dispersion determined by the dependence $\Omega^2 = \Omega_0^2 + V_0^2\kappa^2$ \, the path length in the region 0 < V < V_0 is equal to infinity. In this case the phonon environment follows the charge motion. In the region V > V_0 the soliton motion is accompanied by emission of phonons which leads to a finite path length of a soliton. The latter tends to infinity as $V \rightarrow V_0 + 0$ and $V \rightarrow \infty$. The presence of dissipation leads to a finite soliton path length. An equilibrium velocity of soliton in an external electric field is calculated. It is shown that there is a maximum intensity of an electric field at which a steady motion of a soliton is possible. The soliton mobility is calculated for the stable or ohmic brunch.Comment: 16 pages, 2 figure

The way from high to room temperature superconductivity

Presently, the main method of producing new high-temperature superconductors is chemical when record temperatures of the superconducting transition $T_c$ are reached due to changes in the chemical structure of a superconductor. This paper deals with a possibility to reach room temperatures of $T_c$ in already available high-temperature superconducting materials by physical methods. It is shown that a superconducting phase corresponds to a Bose condensate moving in a thin subsurface layer and a motionless condensate in volume. We discuss a possibility to set in motion a motionless Bose condensate and enhance the temperature of superconducting transition.Comment: 3 page

Phonon interaction of electron in the translation-invariant strong-coupling theory

A dependence of phonon interaction on the interelectronic distance is found for a translation-invariant (TI) strong-coupling bipolaron. It is shown that the charge induced by the electrons in a TI-bipolaron state is always greater than that in a bipolaron with spontaneously broken symmetry.Comment: Modern Physics Letters B, accepted. 5 pages, 2 figure