Evidence for charge delocalization crossover in the quantum critical superconductor CeRhIn₅.

Area of Science:

• Condensed Matter Physics
• Quantum Materials
• Strongly Correlated Electron Systems

Background:

• Heavy-fermion systems exhibit complex magnetic behavior near absolute zero.
• Understanding the interplay between electron localization and delocalization is key to quantum criticality.
• The Kondo effect plays a crucial role in heavy-fermion system properties.

Purpose of the Study:

• To investigate the delocalization of f-electron degrees-of-freedom relative to magnetic quantum critical points (QCPs) in heavy-fermion systems.
• To experimentally determine the finite-temperature scale E_loc signaling the crossover from localized to delocalized f-electron character.
• To differentiate between Kondo-breakdown criticality and spin-density-wave (SDW) criticality.

Main Methods:

• Utilizing pressure-dependent Hall measurements to probe electronic properties.
• Analyzing the behavior of the finite-temperature scale E_loc as a function of pressure.
• Comparing the E_loc(P) behavior in pristine CeRhIn₅ with Sn-doped CeRhIn₅.

Main Results:

• In CeRhIn₅, E_loc(P) extrapolates to zero at the antiferromagnetic QCP, indicating Kondo-breakdown criticality with associated magnetic and charge fluctuations.
• In 4.4% Sn-doped CeRhIn₅, E_loc(P) extrapolates into the magnetically ordered phase, decoupled from the QCP, suggesting SDW criticality with only SDW order parameter fluctuations.
• Superconductivity in both materials reaches maximum critical temperature (T_c) at their respective magnetic QCPs.

Conclusions:

• Experimentally determining E_loc is crucial for characterizing quantum criticality.
• The nature of criticality (Kondo-breakdown vs. SDW) significantly impacts associated fluctuations.
• Understanding these critical fluctuations is essential for elucidating superconductivity mechanisms in heavy-fermion compounds.