Title: Avoided valence transition in a plutonium superconductor

Abstract

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 Tc. 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 T_c, 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 Tcmore » of PuCoGa₅.« less

Authors:

Ramshaw, B. J. ^[1]; Shekhter, Arkady ^[1]; McDonald, Ross D. ^[1]; Betts, Jon B. ^[1]; Mitchell, J. N. ^[2]; Tobash, P. H. ^[2]; Mielke, C. H. ^[1]; Bauer, E. D. ^[2]; Migliori, Albert ^[1]

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+ Show Author Affiliations

1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab)
2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Publication Date:

Tue Mar 03 00:00:00 EST 2015

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Materials Science of Actinides (MSA)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1385669

Grant/Contract Number:  

SC0001089

Resource Type:

Accepted Manuscript

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Volume: 112; Journal Issue: 11; Related Information: MSA partners with University of Notre Dame (lead); University of California, Davis; Florida State University; George Washington University; University of Michigan; University of Minnesota; Oak Ridge National Laboratory; Oregon state University; Rensselaer Polytechnic Institute; Savannah River National Laboratory; Journal ID: ISSN 0027-8424

Publisher:

National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; nuclear (including radiation effects); materials and chemistry by design; synthesis (novel materials); synthesis (self-assembly)