Controlling magnetism in an antiferromagnetic Mott insulator with ultrashort optical pulses can lead to both advances in our fundamental understanding of out-of-equilibrium interacting quantum matter as well as to novel high-speed information storage and processing technologies. However, optically manipulating antiferromagnetic order and detecting its out-of-equilibrium behaviors have proven difficult owing to various factors such as the absence of net magnetization and the ultrafast timescales involved. In this talk, I will describe a novel time-resolved nonlinear optical polarimetry technique that is capable of measuring ultrafast changes in magnetic symmetry. I will then describe how we have deployed this technique to reveal an unusual out-of-equilibrium critical behavior of the magnetic order in an optically pumped Mott insulator that circumvents the laws of equilibrium thermodynamics.

Bio：Prof. David Hsieh is an experimental condensed matter physicist whose research focuses on macroscopic quantum electronic phases of matter in solid state systems. In particular, Prof. Hsieh is interested in developing novel nonlinear optics, time-resolved ultrafast optics and angle-resolved photoemission based spectroscopic probes to search for exotic topological and symmetry-broken quantum phases of matter. Prof. Hsieh earned his B.S in Physics and Mathematics from Stanford University in 2003 and his Ph.D. in Physics from Princeton University in 2009 where he worked on both neutron scattering studies of highly frustrated magnets as well as synchrotron-based spin- and angle-resolved photoemission spectroscopy of topological insulators. From 2009 to 2012 Prof. Hsieh was a Pappalardo Postdoctoral Fellow in Physics at MIT. There he developed several table-top laser-based techniques to study the ultrafast opto-electronic properties of topological insulators and wider classes of correlated spin-orbit coupled systems. He joined the Caltech faculty in 2012. Prof. Hsieh is the recipient of a William L. McMillan Award in condensed matter physics, a Sloan Research Fellowship, a Packard Fellowship in Science and Engineering and a Presidential Early Career Award for Scientists & Engineers.