Berlin 2012 – scientific programme
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O: Fachverband Oberflächenphysik
O 35: Poster Session II (Polymeric biomolecular films; Nanostructures; Electronic structure; Spin-orbit interaction; Phase transitions; Surface chemical reactions; Heterogeneous catalysis; Particles and clusters; Surface magnetism; Electron and spin dynamics; Surface dynamics; Methods; Electronic structure theory; Functional molecules)
O 35.140: Poster
Tuesday, March 27, 2012, 18:15–21:45, Poster B
Magnetism and unusual Cu valence in correlated perovskites — •Paola Alippi1 and Vincenzo Fiorentini2 — 1CNR-ISM, Rome, Italy — 2CNR-IOM and University of Cagliari, Italy
The interplay of the valence states of Cu and of the X cation determines the magnetic and conduction properties of the ACu3X4O12 quadruple perovskites. CaCu3Ti4O12 (CCTO) should be a Mott-like insulator due to the nominal 4+ valence of Ti and 2+ valence of Cu. As Fe and Co prefer greatly a 3+ valence to a 4+ one, LaCu3Fe4O12 (LCFO) and YCu3Co4O12 (YCCO) will be insulating if Cu is 3+. It was suggested that the nominally 3+ Cu state may actually be a “Zhang-Rice singlet” bound state of a ligand hole and a native Cu hole, coupled antiferromagnetically. If however Cu is 3+ and unmagnetized along with its neighbors, neither Mott nor Zhang-Rice physics are at play.
Based on ab initio calculations using several beyond-local density-functional approaches (GGA+U, HSE hybrid, self-interaction correction, G0W0) we confirm the Mott-like nature of CCTO, and show that LCFO is an antiferromagnetic (on the Fe lattice) insulator, while Co adopts a low-spin state and produces a non-magnetic and insulating YCCO. Unexcitingly, neither LCFO or YCCO are Mott or Zhang-Rice-like systems, as Cu therein is strictly non-magnetic and effectively 3+ in valence. CCTO may instead exhibit Zhang-Rice type behavior upon hole doping, progressively emptying its flat Cu-like top valence band.