期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 112, 期 11, 页码 3285-3289出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1421174112
关键词
unconventional superconductivity; heavy fermions; quantum criticality; valence fluctuations; resonant ultrasound spectroscopy
资金
- US Department of Energy, Basic Energy Sciences, Division of Materials Sciences and Engineering
- Los Alamos National Laboratory (LANL) Laboratory Directed Research & Development (LDRD) Program
- National Science Foundation [DMR-1157490]
- State of Florida
The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-T-c cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5-the highest T-c superconductor of the heavy fermions (T-c = 18.5 K)-and find that the bulk modulus softens anomalously over a wide range in temperature above T-c. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high T-c of PuCoGa5.
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