Enhanced dimerization of TiOCl under pressure: spin-Peierls to Peierls transition

Phys Rev Lett. 2009 Feb 6;102(5):056406. doi: 10.1103/PhysRevLett.102.056406. Epub 2009 Feb 6.

Abstract

We report x-ray diffraction and magnetization measurements under pressure combined with ab initio calculations to show that high-pressure TiOCl corresponds to an enhanced Ti3+-Ti3+ dimerized phase existing already at room temperature. Our results demonstrate the formation of a metal-metal bond between Ti3+ ions along the b axis of TiOCl, accompanied by a strong reduction of the electronic gap. The evolution of the dimerization with pressure suggests a crossover from the spin-Peierls to a conventional Peierls situation at high pressures.