Knight shift anomalies and long range order

 The Fate of Heavy Electrons at Low Temperature:

NMR studies of a broad range of heavy electron materials indicate that the shift of the resonance frequency stops tracking the magnetic susceptibility below the onset of the Kondo lattice coherence at a temperature T*.  This anomaly arises because of the formation of a heavy electron component.  Questions have remained, however, as to the fate of the heavy electrons and the remaining local moments at low temperature.  Our studies suggest that different types of order can develop in one or the other channel. For example, in CeRhIn5 the electrons relocalize, whereas in URu2Si2 the heavy electrons are unstable to the hidden order phase.  For details see: “Long range order and two-fluid behavior in heavy electron materials”.