Intermediate valence and spin fluctuations near a quantum critical point in CeRu2-xCoxGe2

We show the presence of a quantum critical point in CeRu2-xCoxGe2 (0 x 2) using detailed heat capacity and muon spin relaxation (& mu;SR) measurements. The millikelvin heat capacity and & mu;SR results for the critical composition xC - 1.5 are consistent with the spin fluctuation model of the quantum critical point. The timefield-temperature scaling of the heat capacity and & mu;SR data further suggests the role of critical and cooperative spin fluctuations near the antiferromagnetic quantum critical point. In addition, the temperature-dependent x-ray absorption near edge structure reveals intermediate valence fluctuation down to the lowest temperature for the compositions x 1.5. The noninteger valence for the critical composition xC - 1.5 is further demonstrated by room temperature x-ray photoelectron spectroscopy. Interestingly, the quantum criticality in CeRu2-xCoxGe2 is governed by the survival of valence and spin fluctuations down to the lowest temperature.