0506706.pdf (1.49 MB)
Strong-coupling theory of high-temperature superconductivity and colossal magnetoresistance
preprint
posted on 2006-04-04, 09:38 authored by A.S. AlexandrovWe argue that the extension of the BCS theory to the strong-coupling regime describes the
high-temperature superconductivity of cuprates and the colossal magnetoresistance (CMR) of ferromagnetic
oxides if the phonon dressing of carriers and strong attractive correlations are taken into
account. The attraction between carriers, which is prerequisite to high-temperature superconductivity,
is caused by an almost unretarted electron-phonon interaction sufficient to overcome the direct
Coulomb repulsion in the strong-coupling limit, where electrons become polarons and bipolarons
(real-space electron or hole pairs dressed by phonons). The long-range Frohlich electron-phonon interaction
has been identified as the most essential in cuprates providing ”superlight” lattice polarons
and bipolarons. A number of key observations have been predicted and/or explained with polarons
and bipolarons including unusual isotope effects, normal state (pseudo)gaps, upper critical fields,
etc. Here some kinetic, magnetic, and more recent thermomagnetic normal state measurements are
interpreted in the framework of the strong-coupling theory, including the Nernst effect and normal
state diamagnetism. Remarkably, a similar strong-coupling approach offers a simple explanation of
CMR in ferromagnetic oxides, while the conventional double-exchange (DEX) model, proposed half
a century ago and generalised more recently to include the electron-phonon interaction, is in conflict
with a number of modern experiments. Among these experiments are site-selective spectroscopies,
which have shown that oxygen p-holes are current carriers rather than d-electrons in ferromagnetic
manganites (and in cuprates) ruling out DEX mechanism of CMR. Also some samples of ferromagnetic
manganites manifest an insulating-like optical conductivity at all temperatures contradicting
the DEX notion that their ferromagnetic phase is metallic. On the other hand, the pairing of oxygen
holes into heavy bipolarons in the paramagnetic phase and their magnetic pair-breaking in the ferromagnetic
phase account for the first-order ferromagnetic phase transition, CMR, isotope effects,
and pseudogaps in doped manganites. Here we propose an explanation of the phase coexistence
and describe the shape of resistivity of manganites near the transition in the framework of the
strong-coupling approach.
History
School
- Science
Department
- Physics
Pages
1560595 bytesPublication date
2005Notes
This is a pre-print. It is also available at: http://arxiv.org/abs/cond-mat/0506706.Language
- en