On the dual role of the d-electrons in iron-pnictides

In the stoichiometric Fe-pnictides the same d-electrons form the local moments and participate in the metallic conductivity. In the manuscript the emergence of the magnetic moments on the Fe-sites, their interaction with the itinerant electrons are studied in the paramagnetic phase at the different relations between the onsite Coulomb repulsion and the intraatomic Hund's exchange. The energy of the local center that is due to its interaction with the conduction electrons is calculated exactly. It is found that the spin density wave transition is controlled by the RKKY interactions between the centers rather than by the nesting mechanism. In the paramagnetic phase the electrons scatter on the randomly oriented moments. The calculated inverse mean free time provides the interpretation for few available experimental data on the conductivity. The multi-band structure of the energy spectrum in iron pnictides is taken into account.Comment: 16 page

The direct Cu NQR Study of the Stripe Phase in the Lanthanum Cuprates

Using Cu NQR in Eu-doped La_(2-x)Sr_xCuO_4 we find the evidence of the pinned stripe phase at 1.3K for 0.08<x<0.18. The pinned fraction increases by one order of magnitude near hole doping x=1/8. The NQR lineshape reveals three inequivalent Cu positions. A dramatic change of the NQR signal for x > 0.18 correlating with the onset of bulk superconductivity corresponds to the depinning of the stripe phase.Comment: 4 pages, 3 figures, to appear in Physica C, Proceedings of the 6th International Conference on Materials and Mechanisms of Superconductivity, Houston, February 200

Anisotropy of the polarizability and steric structure of arylvinyl selenides and arylvinyl sulfides

1. Molecules of arylvinyl selenides have a maximally conjugated planar s-trans structure, 2. The conformations of arylvinyl sulfides are determined by the ratio of the energies of conjugation and steric repulsion of atoms; the disturbance of coplanarity occurs on account of rotation of the aryl radicals. © 1976 Plenum Publishing Corporation

The two-component physics in cuprates in the real space and in the momentum representation

Gradual evolution of two phase coexistence between dynamical and static regimes in cuprates is first investigated in the real space by making use of the available neutron scattering, NMR and mSR data. Analysis of the Hall effect and the ARPES spectra reveals the presence of two groups of charge carriers in LSCO. The T-dependent component is due to the thermal activation of bound electron-hole structures seen near antinodal points in the Brillouin zone, thus introducing the two-component physics also for the momentum representation. Interpretation of so-called "van Hove bands" undergoes drastic changes. Importance of the findings for pseudo-gap physics is stressed. Relation to some recent STM and STS results is discussed.Comment: 8 pages, 6 figures, reported at LEHTSC 2007 conference (Tsukuba), submitted to Journal of Physics: Conference Serie