Regensburg 2007 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 26: Metal-Insulator Transition
TT 26.10: Vortrag
Donnerstag, 29. März 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 d−d 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.