Abstract：In strongly correlated electron materials (SCEM), the delicate interplay between spin, charge, and lattice degrees of freedom often leads to extremely rich phase diagrams exhibiting intrinsic phase inhomogeneities. The key to studying and disentangling such complexities in SCEM usually lies in the characterization and control of the materials at fundamental energy, time and length scales. I will use this opportunity to report the recent advances in the IR and THz spectroscopy and explain how they can be used to probe electronic/structural phase transitions with unprecedented spatial and temporal resolutions. Specifically, with scanning near-field infrared microscopy we resolved the insulator to metal phase transitions in SCEM such as VO2, Ca2RuO4 with ~10 nm resolution over a broad spectral range (350 cm-1 to 2500 cm-1). I will also discuss the future development of near-field scanning microscope including the cryogenic capabilities and its coupling to ultrafast pump probe spectroscopy. These results set the stage for future spectroscopic investigations to access the fundamental properties of complex materials.

Bio: Mengkun Liu (Ph.D. 2012 Boston University) is an assistant professor at the Physics Department of Stony Brook University (since Jan. 2015). His post doc research is at UC San Diego from 2012-2014. His research interests include physics of correlated electron systems, two-dimensional materials, infrared nano-optics and ultrafast time domain spectroscopy.  Prizes include Seaborg Institute Research Fellowships at Los Alamos National Lab (2009, 2010).