Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 9: Correlated Electrons: Metal-Insulator Transition 1

TT 9.10: Vortrag

Montag, 23. März 2009, 16:30–16:45, HSZ 03

Predicting pressure-induced phase transitions in the Mott insulator TiOCl — Yuzhong Zhang, •Harald O. Jeschke, and Roser Valenti — Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany

The layered Mott insulator TiOCl has been the focus of a lot of recent experimental and theoretical research as it is one of the few inorganic spin-Peierls materials. Still, several important issues remain unsettled, namely the underlying Hamiltonian, the mechanism that is responsible for the incommensurate phase and the nature of the high-pressure phases. We performed thorough density functional theory calculations in order to shed light on these issues. First, we determine the parameters of a very general spin-phonon Hamiltonian[1]. The resulting model for TiOCl has strong antiferromagnetic exchange couplings along one direction with weak but significant frustrating ferromagnetic couplings along the other two directions, and it has strong spin-lattice coupling constants. Using constant pressure Car Parrinello molecular dynamics calculations, we determine the high pressure structures of TiOCl from first principles[2]. We predict two consecutive phase transitions, first from a Mott insulating high symmetry structure to a metallic dimerized structure and then back to a metallic high symmetry structure. The first of the two transitions has since been confirmed by experiment.

[1] Y. Z. Zhang, H. O. Jeschke, and R. Valentí, Phys. Rev. B 78, 205104 (2008).

[2] Y. Z. Zhang, H. O. Jeschke, and R. Valentí, Phys. Rev. Lett. 101, 136406 (2008).