Pressure-induced anomalous valence crossover in cubic YbCu(5)-based compounds

A pressure-induced anomalous valence crossover without structural phase transition is observed in archetypal cubic YbCu(5) based heavy Fermion systems. The Yb valence is found to decrease with increasing pressure, indicating a pressure-induced crossover from a localized 4f (13) state to the valence fluctuation regime, which is not expected for Yb systems with conventional c–f hybridization. This result further highlights the remarkable singularity of the valence behavior in compressed YbCu(5)-based compounds. The intermetallics Yb(2)Pd(2)Sn, which shows two quantum critical points (QCP) under pressure and has been proposed as a potential candidate for a reentrant Yb(2+) state at high pressure, was also studied for comparison. In this compound, the Yb valence monotonically increases with pressure, disproving a scenario of a reentrant non-magnetic Yb(2+) state at the second QCP.