Pressure dependence of Ce valence in CeRhIn₅.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Cerium (Ce) compounds exhibit complex electronic behavior due to the proximity of 4f and conduction electron states.
• Pressure-induced changes in Ce valence are crucial for understanding phenomena like heavy fermion behavior and quantum criticality.
• CeRhIn5 is a model system for studying these effects, with theoretical predictions of a valence crossover.

Purpose of the Study:

• To experimentally determine the Ce valence in CeRhIn5 as a function of applied pressure at different temperatures.
• To investigate the robustness of the Ce valence against pressure and compare with theoretical models.
• To establish an upper limit for pressure-induced Ce valence changes in this material.

Main Methods:

• X-ray absorption spectroscopy (XAS) was employed to probe the Ce valence state.
• Measurements were performed in partial fluorescent yield (PFY) mode for enhanced surface sensitivity.
• Experiments were conducted at two distinct temperatures: 300 K (room temperature) and 22 K.

Main Results:

• At 300 K, no significant change in Ce valence (>0.01) was observed up to 5.5 GPa.
• At 22 K, the Ce valence remained stable and robust against pressure below 6 GPa.
• These experimental findings contradict the theoretically predicted valence crossover at approximately 2.35 GPa.

Conclusions:

• The study provides experimental evidence that the Ce valence in CeRhIn5 is remarkably stable under pressure at both investigated temperatures.
• The results suggest that the current theoretical framework for critical valence fluctuations in CeRhIn5 may require revision.
• An upper limit for the pressure-induced change in Ce valence was established, offering critical data for future theoretical modeling.