898 research outputs found
Band splitting and relative spin alignment in bilayer systems
Influence of relative spin alignment on the band splitting and magnetic
excitations in the bilayer correlated systems is studied. Splitting occures to
be large or small depending on orientation of staggered spins of layers. Change
of the ground state configuration with doping is shown. Behavior of the bilayer
splitting in Bi-based cuprate allows to suppose that superconducting transition
is accompanied by transformation of spin configuration of system.Comment: 9 pages, 3 figure
Proton configurations in the hydrogen bonds of KH2PO4 as seen by resonant x-ray diffraction
KH2PO4 (KDP) belongs to the class of hydrogen-bonded ferroelectrics, whose
paraelectric to ferroelectric phase transition is driven by the ordering of the
protons in the hydrogen bonds. We demonstrate that forbidden reflections of
KDP, when measured at an x-ray absorption edge, are highly sensitive to the
asymmetry of proton configurations. The change of average symmetry caused by
the "freezing" of the protons during the phase transition is clearly evidenced.
In the paraelectric phase, we identify in the resonant spectra of the forbidden
reflections a contribution related to the transient proton configurations in
the hydrogen bonds, which violates the high average symmetry of the sites of
the resonant atoms. The analysis of the temperature dependence reveals a change
of relative probabilities of the different proton configurations. They follow
the Arrhenius law, and the activation energies of polar and Slater
configurations are 18.6 and 7.3 meV, respectively
The Fermi surface reconstruction in stripe phases of cuprates
Mean-field study of the stripe structures is conducted for a hole-doped
Hubbard model. For bond-directed stripes, the Fermi surface consists of
segments of an open surface and the boundaries of the hole pockets which appear
in the diagonal region of momenta under certain conditions. Segments of the
first type are due to one-dimensional bands of states localized on the domain
walls. The relation of bands to the doping and temperature dependences of the
Hall constant is discussed. In connection with the observation of quantum
magnetic oscillations, a systematic search for the electron pockets has been
carried out. It is shown that the formation of such pockets in bilayer models
is quite possible.Comment: 4 pages, 3 figure
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