Transition metal compounds under pressure - Karl Syassen - 7 octobre 2015

Karl Syassen, Max Planck Institut für Festkörperforschung, Stuttgart

Mercredi 7 octobre 2015 à 10 h 30

IMPMC, Université P. et M. Curie, 4, Place Jussieu, 75005 Paris

Salle du Conseil - Barre 23-24 - 5^e étage - Salle 502

Abstract

The main focus of this presentation will be on the effect of pressure on structural and electronic properties of transition metal compounds located near the insulator-metal
borderline. The experiments consist of a combination of high-resolution synchrotron diffraction and optical spectroscopy at moderate pressures (40 GPa). The physics concerns the behavior of correlated electrons in systems with transition metal ions in high oxidation states, in particular the interplay between major or subtle changes in atomic arrangements, electron delocalization, and related effects like phonon anomalies. After briefly recalling general aspects of correlated-electron physics and outlining motivations for high pressure experiments, several examples will be addressed. Among them are the pressure-driven orbital rearrangement and insulator to metal transition in perovskite-type titanites, the insulator to metal transition presumably due to an oxidation state change in one of the multiferroic spinels (CdCr2S4), and a structural instability mode of high-Tc cuprate superconductors leading to a change of crystal symmetry along with a near-loss of superconducting behavior.