Title: Correlated Electron Materials Manifested by Broken Symmetry

Lecturer: Jiandi Zhang,Florida International University, Miami, Florida, USA

Abstract: Many emergent and collective phenomena, such as high-temperature superconductivity, “colossal” magnetoresistance, charge/orbital ordering, and quantum criticality, have been revealed in transition-metal oxide (TMO) materials, a class of fascinating “correlated electron” systems. The signature of these materials is the multitude of competing ground states that can be tuned or manipulated by doping, structural manipulations, strain induction, or the application of external stimulus, such as pressure, electric or magnetic fields, etc. On the other hand, creating surfaces, interfaces, thin films, and artificial superstructures add the additional twists of ‘man-made’ dimensions, approaching the quantum phenomena of correlated materials with broken symmetry and reduced dimensionality. New physics and new functionality may appear, thus offering an opportunity for new discovery and new technological implication.
In this talk, I will briefly review few of fascinating phenomena revealed in TMOs. I will focus on an interesting layered TMO material: Ca2-xSrxRuO4. It shows a rich phase diagram and variety of ground states from a Mott insulator (Ca2RuO4), quantum criticality (Ca1.5Sr0.5RuO4), to spin-triplet superconductor (Sr2RuO4), accompanied with a continuous evolution of lattice distortion. Particularly I will discuss several new phenomena observed at the crystal surfaces, including surface reconstruction which may stabilize magnetic ordering, unusual surface Mott-insulator transition, anomalous depression in density of states close to the Fermi energy, and electronic nano-phase separation, presenting new emergent physics manifested by reduced dimensionality and broken symmetry.
This work was supported by US National Science Foundation and Department of Energy.

Time: 9:00am,June 27, 2008
Place:B203