Colloquium on May 21, 2012

Hidenori Takagi
Department of Physics, University of Tokyo

Emergent phases of correlated electrons in transition metal oxides

The electric and magnetic properties of transition metal oxides are often dominated by electrons in d-orbitals. Large Coulomb repulsion between electrons accommodated in the spatially constrained d-orbitals tends to block the motion of electrons from one atom to another, and the electrons are highly entangled. Just like interacting atoms and molecules, the entangled electrons, called correlated electrons, form solid (insulator), liquid (metal), and superfluid (superconductor) states inside the solid. The presence of the three degrees of freedom attached to electrons – charge, spin and orbital, enrich these electronic phases further. A variety of phases, with complex combinations of charge, spin, and orbital ordered states, indeed appear in the phase diagrams of transition metal oxides.  I will talk about selected topics on such exotic phases of correlated electrons, including nano-stripes in cuprates, quantum liquid states of spins and charges in spinel related oxides and spin-orbit coupling induced phases in heavy 5d transition metal oxides. Finally, I will briefly discuss the possible device functions coming out of the concept of electronic phases, with emphasis on phase change functions.