arXiv subjects

A. S. Alexandrov

Publications and source records attributed to A. S. Alexandrov.

131 records · Page 8Linked to original sources

arXiv1996

Logarithmic divergence of normal state resistivity of bipolaronic high-$T_{c}$ cuprates

The resonance Wigner scattering of charged bosons (small bipolarons) in a random potential leads to logarithmically divergent low-temperature resistivity as observed in several cuprates. Unusual temperature dependence of resistivity of $La_{2-x}Sr_{x}CuO_{4}$ as well as of the Hall effect is quantitatively described in a wide temperature range providing an evidence for $2e$ charged Bose-liquid in high-$T_{c}$ cuprates.

cond-mat.supr-con↗

arXiv1996

Coherent `ab' and `c' transport theory of high-$T_{c}$ cuprates

We propose a microscopic theory of the `$c$'-axis and in-plane transport of copper oxides based on the bipolaron theory and the Boltzmann kinetics. The fundamental relationship between the anisotropy and the spin susceptibility is derived, $ρ_{c}(T,x)/ρ_{ab}(T,x)\sim x/\sqrt{T}χ_{s}(T,x)$. The temperature $(T)$ and doping $(x)$ dependence of the in-plane, $ρ_{ab}$ and out-of-plane, $ρ_{c}$ resistivity and the spin susceptibility, $χ_{s}$ are found in a remarkable agreement with the experimental data in underdoped, optimally and overdoped $La_{2-x}Sr_{x}CuO_{4}$ for the entire temperature regime from $T_{c}$ up to $800K$. The normal state gap is explained and its doping and temperature dependence is clarified.

cond-mat↗

arXiv1996

Boson-fermion model beyond mean-field approximation

A model of hybridized bosons and fermions is studied beyond the mean field approximation. The divergent boson self-energy at zero temperature makes the Cooper pairing of fermions impossible.The frequency and momentum dependence of the self- energy and the condensation temperature $T_{c}$ of initially localized bosons are calculated analytically. The value of the boson condensation temperature $T_{c}$ is below $1K$ which rules out the boson-fermion model with the initially localized bosons as a phenomenological explanation of high-temperature superconductivity. The intra-cell density-density fermion-boson interaction dominates in the fermion self-energy. The model represents a normal metal with strongly damped bosonic excitations. The latter play the role of normal impurities.

cond-mat↗

arXiv1996

Theory of Superconducting $T_{c}$ of doped fullerenes

We develop the nonadiabatic polaron theory of superconductivity of $M_{x}C_{60}$ taking into account the polaron band narrowing and realistic electron-phonon and Coulomb interactions. We argue that the crossover from the BCS weak-coupling superconductivity to the strong-coupling polaronic and bipolaronic superconductivity occurs at the BCS coupling constant $λ\sim 1$ independent of the adiabatic ratio, and there is nothing ``beyond'' Migdal's theorem except small polarons for any realistic electron-phonon interaction. By the use of the polaronic-type function and the ``exact'' diagonalization in the truncated Hilbert space of vibrons (``phonons'') we calculate the ground state energy and the electron spectral density of the $C_{60}^{-}$ molecule. This allows us to describe the photoemission spectrum of $C_{60}^{-}$ in a wide energy region and determine the electron-phonon interaction. The strongest coupling is found with the high-frequency pinch $A_{g2}$ mode and with the Frenkel exciton. We clarify the crucial role of high-frequency bosonic excitations in doped fullerenes which reduce the bare bandwidth and the Coulomb repulsion allowing the intermediate and low-frequency phonons to couple two small polarons in a Cooper pair. The Eliashberg-type equations are solved for low-frequency phonons. The value of the superconducting $T_{c}$, its pressure dependence and the isotope effect are found to be in a remarkable agreement with the available experimental data.

cond-mat↗

arXiv1995

The de Haas-van Alphen effect in canonical and grand canonical multiband Fermi liquid

A qualitatively different character of dHvA oscillations has been found in a multiband (quasi)two dimensional Fermi liquid with a fixed fermion density $n_{e}$ (canonical ensemble) compared with an open system where the chemical potential $μ$ is kept fixed (grand canonical ensemble). A new fundamental period $P_{f}$ appears when $n_{e}$ is fixed, a damping of the Landau levels is relatively small and a background density of states is negligible. $P_{f}$ is determined by the total density rather than by the partial densities of carriers in different bands: $P_{f}=1/(2n_{e}ϕ)$ for spin-split Landau levels and $P_{f}=1/(n_{e}ϕ)$ in the case of spin degenerate levels where $ϕ$ is the flux quantum.

mtrl-th↗