Unusual electronic structure of PrBa2Cu3O7.

摘要: A model for the electronic structure of ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ is proposed with three independent components: insulating ${\mathrm{CuO}}_{2}$ planes oxidation state ${\mathrm{Cu}}^{\mathrm{II}}$, mixed valent Pr ions almost equal numbers ${\mathrm{Pr}}^{\mathrm{III}}$ and ${\mathrm{Pr}}^{\mathrm{IV}}$, ${\mathrm{CuO}}_{3}$ chains described by a t-J filling \ensuremath{\approxeq}1/2. The difference from high-${\mathit{T}}_{\mathit{c}}$ superconductors comes an enhanced stability ${\mathrm{Pr}}^{\mathrm{IV}}$ due to hybridization O neighbors, involves transfer holes primarily planar 2${\mathit{p}}_{\mathrm{\ensuremath{\sigma}}}$ 2${\mathit{p}}_{\mathrm{\ensuremath{\pi}}}$ states. nature ascribed extreme sensitivity dc conductivity vacancies impurities.