Abstract
A pressure-induced anomalous valence crossover without structural phase transition is observed in archetypal cubic YbCu5 based heavy Fermion systems. The Yb valence is found to decrease with increasing pressure, indicating a pressure-induced crossover from a localized 4f13 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 YbCu5-based compounds. The intermetallics Yb2Pd2Sn, which shows two quantum critical points (QCP) under pressure and has been proposed as a potential candidate for a reentrant Yb2+ 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 Yb2+ state at the second QCP.
Highlights
A pressure-induced anomalous valence crossover without structural phase transition is observed in archetypal cubic YbCu5 based heavy Fermion systems
Physical properties in the valence fluctuation systems can be understood in terms of a competition between the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction and the Kondo effect, both are originated by interaction between f and conduction (c) electrons[1, 2]
A scenario based on the single impurity Anderson model (SIAM) taking into account a pressure-induced enhancement of valence fluctuations at low pressure and suppression at high pressure was suggested to explain the two QCPs17
Summary
The pressure dependence of A below 4 GPa was reported to show a divergent behavior with pressure; above 5 GPa a non-Fermi liquid state was predicted[13] This suggests that there might be a QCP in cubic YbCu5 around 5–6 GPa. In YbCu2Si2 The actual change of the Kondo temperature with pressure can be more complex, this pressure-induced enhancement of T0, which stabilizes the nonmagnetic f 14 state, may be one possible explanation for the decrease of the Yb valence in YbCu5-based compounds under pressure. The anomalous valence transition in YbxFe4Sb12 and YbMn6Ge6 were not understood by a normal Kondo-lattice picture Instead, it was necessary taking into account the effect of distinct band structure features or of magnetism related to d electrons. Low-temperature data for the Ag-substituted systems may be helpful to understand the pressure-induced anomalous valence transition of the Yb systems and the Kondo physics under pressure
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