摘要：In this colloquium, I describe the most recent progress in the field of iron-based superconductors.  Using neutron scattering as a probe, we study spin excitations in FeAs-based superconductors and its undoped parent compounds.  For the undoped CaFe2As2, we determine the entire spin wave dispersion curve and show that magnetic exchange coupling has strong in-plane exchange anisotropy with no evidence for Stoner continuum.  Upon doping to induce superconductivity, we find that the spin excitations spectrum is dominated by a large spin gap and a neutron spin resonance.  We show that the resonance is directly connected with superconducting electronic gap.  These results suggest that spin excitations are the most promising candidate for electron pairing and superconductivity in iron-based superconductors. 

报告人简介：Pengcheng Dai obtained his Ph. D degree from University of Missouri-Columbia in 1993.  From 1993-1996 he was a postdoc associate at Oak Ridge Natinal laboratory.  From 1996-2001, he was a staff scientist at Oak Ridge National Laboraty.  From 2001-2006, he became an associate professor and joint faculty of The University of Tennessee and Oak Ridge National Laboraty.  From 2006, he was promoted to full professor.  From 2008, he was promoted to Joint Institute of Advanced Materials Chair of Excellence and Professor of Physics.  From 2009, he also established a group at Institute of Physics, CAS, focuses on developing neutron scattering techniques in China.  He is an APS fellow from 2008.   His research interest focues on using neutron scattering as a probe to study strongly correlated electron materials including understanding the interplay between magnetism and superconductivity.