Unusual electronic phase transitions in transition metal oxides
Ralph Claessen, 
Experimentelle Physik IV, Universität Würzburg

In transition metal oxides the cooperative interplay between charge,
spin, orbital, and lattice degrees of freedom often leads to transitions
into unsual electronic and/or magnetic phases, thereby giving rise to
novel materials properties and functionalities. A prominent example is
the so-called "Verwey transition" in the mixed-valent oxide Fe3O4
("magnetite") which for decades has been viewed as the prototypical
charge ordering system. I will discuss how recent experimental results
are suggesting a new perspective on the Verwey transition in which
multiorbital correlations and a strong coupling to the lattice are the
dominating factors. My second example concerns an unsual spin-Peierls
transition in the oxohalogenide TiOCl, where low dimensionality adds
another aspect to the complex materials properties.