Quantum continuum fluctuations in glassy perovskite Ca(Co${}_{0.15}$Ru${}_{0.85}$)O${}_3$

Abstract

The quantum spin continuum and classical spin freezing, associated with a glassy state, represent two opposite extremes of a correlated electronic material. Here, we report the coexistence of a quantum spin continuum with a weak spin glass order in Co-doped CaRuO${}_3$ perovskite near the chemical doping dependent metal-insulator transition boundary. Inelastic neutron measurements on Ca(Co${}_{0.15}$Ru${}_{0.85}$)O${}_3$ at low temperature, $T$ = 1.5 K, reveal a continuum spectrum in the $Q-E$ space due to uncorrelated spin fluctuations. This persists across the glass transition at $T_G\simeq$23 K. Furthermore, scaling of the dynamic susceptibility yields a very small scaling coefficient $\hat{I}\pm$ $\simeq$ 0.1, suggesting extreme locality of the dynamic properties. The experimental results indicate the realization of a narrow regime where the distinction between continuum dynamic behavior and glass-like regimes is reduced.

6 pages, 4 figures