Abstract：

　　If you have taught or attended a condensed matter physics course, you know that the subjects are compartmentalized: lattice structure, electronic structure, lattice dynamics, magnetism and superconductivity.  The modern world of functional materials is not compartmentalized; it is the nonlinear entanglement of lattice, electron, and spin degrees of freedom that creates functionality, such as superconductivity, magnetoresistance, quantum criticality, etc..  Functional materials respond to external and internal stimuli, like temperature, pressure, field, or doping.  The goal of materials research is to learn to manipulate, control, or design the desired functionality.  One way to reveal new (hidden) phases in bulk is to explore the functionality of surfaces in an environment of broken symmetry.  Our group has investigated the surface properties of many complex materials, including Fe-based superconductors. In this talk, I will describe the surface properties of Mn-doped double layered ruthenate, Sr3Ru2O7. The bulk parent compound is a paramagnetic metal, but pressure creates a ferromagnetically ordered state and magnetic field drives the material into a quantum critical state.  Mn doping creates a metal-insulator transition and a long range, antiferromagnetically (AFM) ordered state at low temperatures.  The surface, because of structural reconstruction, displays fundamentally different behavior from bulk—insulating when the bulk is conducting and visa versa. Most intriguing is the observation that at the Mn doping where AFM exists in the bulk (low temperatures), AFM order removes the surface reconstruction and results in a surface metal-to-insulator transition resembling a Slater transition, not a Mott transition. Our work shows that crating a surface by breaking the translational symmetry is an effective way to reveal hidden phases non-existent in bulk.

Biosketch：

　　Prof. Ward Plummer received a Bachelor of Arts degree from Lewis and Clark College in 1962 and his Ph. D. degree in Physics from Cornell University in 1968. After working at the National Bureau of Standards until 1973, he joined the faculty at University of Pennsylvania. In 1993, he moved to Tennessee with a joint appointment at the University of Tennessee (Distinguished Professor), Knoxville, and Oak Ridge National Laboratory (Distinguished Scientist). He was the director of the Joint Institute for Advanced Materials (JIAM) until he came to Louisiana State University in 2009. He is a Boyd Professor of Physics and Astronomy, and special assistant to the Vice President for Research.

　　As an eminent scientist in Condensed Matter Physics, Prof. Plummer has developed advanced high-resolution observation methods, focused on investigations of the phenomena associated with the unique environment at a surface or interface. He is author of >400 refereed papers. He was elected to the US National Academy of Sciences in 2006 and the American Academy of Arts and Sciences in 2014. He was awarded various prizes, including Wayne B. Nottingham Prize (1968), Davisson-Germer Prize in Surface Physics (1983), Medard W. Welch Award (2001), and the Award for International Scientific Cooperation from the president of China  (2018).