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Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 26: Metal-Insulator Transition

TT 26.10: Talk

Thursday, March 29, 2007, 16:30–16:45, H19

Spin Peierls Instability, Bond Formation and Orbital Ordering in MgTi2O4 — •Stefano Leoni, Luis Craco, Miriam Schmitt, and Helge Rosner — MPI CPfS, Dresden, Germany

The spinel titanate MgTi2O4 undergoes a metal-insulator transition on cooling below Tc= 270 K, with a symmetry lowering from cubic to tetragonal and a collective mutual rotation of the TiO6 octahedra. This is accompanied by a reorganization of the bonding pattern, which results in bond formation and bond elongation in distinct directions. Also in this titanate, electronic correlation effects, structural distortions and bond breaking pattern are intertwinned and concur to determine the physics of the system. Here we present an electronic structure study of the metal-insulator transition, showing that the latter can be nicely captured by an LDA+U approach. Furthermore, we demonstrate the first order character of the transition, that reflects a complex pattern of bond formation and bond breaking, which modifies the Ti-Ti dd hopping contributions. In our calculations the onsite-potential U works as a source of local asymmetry at the titanium sites. Along this line, structural distortions and electronic correlation effects can be decoupled, allowing for a closer elucidation of the symmetry lifting across the transition. This in turn allows to follow the onset of orbital ordering from a situation of full degeneracy to a reorganized structures, with changed bond formation.
The Emmy-Noether program is acknowledged for financial support. SL acknowledges the Swiss National Science Foundation for funding.

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