Charge redistribution and properties of high-temperature superconductors.

Abstract

We show that in high-${\mathit{T}}_{\mathit{c}}$ superconductors (HTSC) with two groups of electrons (e.g., holes in ${\mathrm{CuO}}_{2}$ planes and in a ``reservoir'') there should exist a charge redistribution with the temperature: the hole concentration ${\mathit{N}}_{\mathit{h}}$ in ``active'' superconducting ${\mathrm{CuO}}_{2}$ planes increases below ${\mathit{T}}_{\mathit{c}}$. This effect may explain structural changes such as the shift of the apical oxygen atom, anomalous thermal expansion, the shift of nuclear quadrupole resonance lines, the change of the positron lifetime, and the modification of the ion channeling below ${\mathit{T}}_{\mathit{c}}$. Some other possible consequences of the charge redistribution (the modification of the temperature dependence of a gap \ensuremath{\Delta} and of the ratio 2${\mathrm{\ensuremath{\Delta}}}_{0}$/${\mathit{T}}_{\mathit{c}}$, the phenomena at a contact of HTSC with normal metals and semiconductors) are discussed.