Neutrons as a probe of hidden order in condensed matter systems

Prof. C. R. Wiebe
University of Winnipeg/University of Manitoba

Early in the development of condensed matter science as a discipline, it became clear that many “model” systems, from water ice to liquid helium, were actually exhibiting ground states that were difficult to characterize with various experimental probes. These so-called “hidden order” states had the signature of an entropy release that was not consistent with theoretical predictions. In the case of water ice, this lead to the “residual entropy” problem made famous by Pauling, and in the case of liquid helium, the low-temperature heat capacity anomaly was indicative of a transition to a superfluid phase. In this talk, I will describe how these various “hidden order” problems have shaped modern ideas in condensed matter, and I will focus specifically on examples of “hidden order” seen in heavy fermion metals, geometrically frustrated materials, and even the high-T_C cuprates. Neutron scattering, in particular, has been a very powerful probe for these fascinating states of matter.