13 research outputs found
Effect of screening of the electron-phonon interaction on the temperature of Bose-Einstein condensation of intersite bipolarons
Here we consider an interacting electron-phonon system within the framework
of extended Holstein-Hubbard model at strong enough electron-phonon interaction
limit in which (bi)polarons are the essential quasiparticles of the system. It
is assumed that the electron-phonon interaction is screened and its potential
has Yukawa-type analytical form. An effect of screening of the electron-phonon
interaction on the temperature of Bose-Einstein condensation of the intersite
bipolarons is studied for the first time. It is revealed that the temperature
of Bose-Einstein condensation of intersite bipolarons is higher in the system
with the more screened electron-phonon interaction.Comment: 6 pages, 4 figure
Polaron features for long-range electron-phonon interaction
The polaron features for long-range electron-phonon interaction are
investigated by extending a variational approach previously proposed for the
study of systems with local coupling. The ground-state spectral weight, the
average kinetic energy, the mean number of phonons, and the electron-lattice
correlation function are discussed for a wide range of model parameters
focusing on the adiabatic regime and comparing the results with the short-range
case (Holstein model). A strong mixing of electronic and phononic degrees of
freedom for small values of the electron-phonon coupling constant is found in
the adiabatic case due to the long-range interaction. Finally a polaron "phase
diagram" is proposed.Comment: 4 figs., to appear in J. Phys.:Condens. Matte
Electronic specific-heat anomalies in high-\u3ci\u3eT\u3csub\u3ec\u3c/sub\u3e\u3c/i\u3e cuprates
In this work, we study the electronic specific heat of underdoped to overdoped high- cuprates, and identify the nature of anomalies in at the superconducting transition temperature and at temperatures above . The doped cuprate superconductor is considered as a multi-carrier model system which is composed of different types of charge carriers. The normal-state electronic specific heat of high- cuprates below a characteristic pseudogap (PG) temperature is calculated taking into account three contributions coming from the excited components of Cooper pairs, the ideal Bose-gas of incoherent Cooper pairs and the unpaired carriers in the impurity band. Above , two contributions to coming from the unpaired intrinsic and extrinsic polarons are calculated within the two-component degenerate Fermi-gas model. The total electronic specific heat below is calculated by considering the contribution and the contribution coming from the superfluid bosonic carriers. We have shown that our theoretical predictions of the behaviors of near and above are strikingly similar to the behaviors of the electronic specific heat observed below and above in LSCO and YBCO. There is fair quantitative agreement between theoretical predictions about the anomalies in (i.e. a -like anomaly near and a BCS-type anomaly above near ) and experimental data
Effect of screening of the electron-phonon interaction on mass renormalization and optical conductivity of the extended Holstein model polarons
An interacting electron-phonon system is considered within the Extended
Holstein model at strong coupling regime and nonadiabatic approximation. It is
assumed that screening of an electron-phonon interaction is due to the excess
electrons in a lattice. An influence of the screening on the mass and optical
conductivity of a lattice polarons is studied. A more general form Yukawa-type
electron-phonon interaction potential potential is accepted and corresponding
forces are derived in a lattice. It is emphasized that the screening effect is
more pronounced at the values of screening radius comparable with a lattice
constant. It is shown that the mass of a lattice polaron obtained using
Yukawa-type electron-phonon interaction potential is less renormalized than
those of the early studied works at the same screening regime. Optical
conductivity of lattice polarons is calculated at different screening regimes.
The screening lowers the value of energy that corresponds to the peak of the
optical conductivity curve. The shift (lowering) is more pronounced at small
values of screening radius too. The factors that give rise to this shift is
briefly discussed.Comment: 8 pages, 10 figures, 1 table. arXiv admin note: substantial text
overlap with arXiv:1308.219