Seminars Archive

Lattice compression as a result of charge carrier localization in HTSC cuprates and MxTiX2 intercalates

Abstract
Two groups of materials are considered: high temperature superconducting cuprates and intercalation compounds of transition metals and silver on a base of titanium dichalcogenides. These materials demonstrate nontrivial physical properties (superconductivity, electronic and chemical phase separation) because of strong mutual influence of the electronic and atomic subsystems. Charge carriers for these materials (or at least part of them) are localized with participation of lattice deformation in form of isotropic volume compression in spite of strong crystal anisotropy of considered layered materials. The temperature range was found experimentally (using X-ray and neutron diffraction, inelastic neutron scattering, electric and magnetic properties) where lattice compression becomes enhanced being accompanied by phonon softening; this temperature area is determined only by the type of the material and not by charge carrier concentration. Such an unusual behavior we explain as a result of enhancement of charge carrier localization degree as a function of temperature. Observed phonon softening is small being masked by concurrent hardening due to lattice compression. Suggested explanation needs in an experimental proof of a change of localization degree for charge carriers in a specific temperature range, in particular, by spectral methods.