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Shining (low frequency) light on quantum magnets: Ising spin chains, quantum spin ice, and spin-orbital liquids

Peter Although typically we regard optical spectroscopies as probes of electronic degrees of freedom in materials, light's time-varying magnetic field allows one to couple to magnetic degrees of freedom.  This talk will review recent advances in the area of time-domain THz spectroscopy and its application to “quantum" magnets.  Our high signal to noise, routinely excellent energy resolution, polarization sensitivity, and unique ability to measure complex response functions gives particular insight into the magnetic response of quantum materials and gives several distinct advantages in these matters over neutron scattering.  I will give examples of the use of the technique on quantum magnet systems as diverse as 1D Ising spin chains, quantum spin ices, and spin-orbital liquids.

N. Peter Armitage has been on the faculty of the Department of Physics and Astronomy at Johns Hopkins University since 2006. He received his bachelor’s degree in Physics from Rutgers University in 1994 and his Ph.D. from Stanford University in 2002.   He is a physicist whose research centers on material systems which exhibit coherent quantum effects at low temperatures, like superconductors and "quantum" magnetism.  Dr. Armitage's principal scientific interest is understanding how is it that large ensembles of strongly interacting, but fundamentally simple particles like electrons in solids act collectively to exhibit complex emergent quantum phenomena.  He is exploiting (and developing) recent technical breakthroughs using very low frequency microwave and THz range radiation to probe these systems at their natural frequency scales.   The material systems of interest require new measurement techniques as their relevant frequencies typically fall between the range of usual optical and electronic methods.  He has been the recipient of a DARPA Young Faculty Award, an NSF Career Award, a Sloan Research Fellowship, was a three time Kavli Frontiers Fellow, the William Spicer Award from the Stanford Synchrotron Radiation Laboratory, the William L. McMillan Award from the University of Illinois and was the co-chair of the 2014 Gordon Research Conference in Correlated Electron Systems.