Pressure-induced valence crossover in superconducting CeCu2Si2

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Heavy fermion compounds like CeCu(2)Si(2) exhibit unique electronic properties due to strong electron correlations.
• Superconductivity in CeCu(2)Si(2) is linked to critical valence fluctuations, particularly near a second superconducting dome under pressure.
• Understanding Ce valence is crucial for elucidating novel pairing mechanisms in these materials.

Purpose of the Study:

• To quantitatively measure the Cerium (Ce) valence in CeCu(2)Si(2) under pressure at low temperatures (14 K).
• To investigate the relationship between Ce valence, pressure, and the proximity to the superconducting region.
• To explore the role of valence fluctuations in potential new superconducting pairing mechanisms.

Main Methods:

• High-resolution partial-fluorescence yield (PFY) measurements at the Ce L(3) edge.
• Analysis of spectral data using the Anderson impurity model for quantitative valence estimation.
• In-situ pressure application and low-temperature measurements (T=14 K).

Main Results:

• A clear increase in Ce valence was observed with applied pressure.
• The electron transfer was found to be weak, indicating a continuous valence change.
• The study suggests a crossover regime rather than a sharp transition in valence.

Conclusions:

• The observed continuous valence change under pressure points towards a crossover regime.
• The hypothetical valence line appears to terminate at a critical endpoint close to absolute zero (T(cr) ≈ 0 K).
• These findings provide insights into the complex interplay between valence, pressure, and superconductivity in heavy fermion systems.