Identification of low-lying energy states in quantum critical Ce(Fe_0.76Ru_0.24)₂Ge₂

The compound Ce(Fe_0.76Ru_0.24)₂Ge₂ has long been known to be a quantum critical point system. One of the features discovered in this material is hyperscaling of the dynamic response of the system. Chemical doping is used to prepare the system at the quantum critical point, which results in a distribution of local Kondo temperatures and consequently the formation of magnetic clusters. We present direct evidence for the spin-flipping of these magnetic clusters, which provides the low energy states required to explain the hyperscaling at the quantum critical point. The superspin flipping was first identified using spin-polarized neutron spectroscopy on the BT7 triple-axis spectrometer at the NIST Center for Neutron Research, then—once the magnetic signal was separated from that of the lattice—tracked using unpolarized neutron spectroscopy on the TRIAX thermal neutron triple-axis spectrometer at the University of Missouri Research Reactor.