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.
