Extended Nuclear Quadrupole Resonance Study of the Heavy-Fermion Superconductor PuCoGa${}_5$

Abstract

PuCoGa${}_5$ has emerged as a prototypical heavy-fermion superconductor, with its transition temperature ($T_c\simeq 18.5$ K) being the highest amongst such materials. Nonetheless, a clear description as to what drives the superconducting pairing is still lacking, rendered complicated by the notoriously intricate nature of plutonium's 5$f$ valence electrons. Here, we present a detailed ${}^{69,71}$Ga nuclear quadrupole resonance (NQR) study of PuCoGa${}_5$, concentrating on the system's normal state properties near to $T_c$ and aiming to detect distinct signatures of possible pairing mechanisms. In particular, the quadrupole frequency and spin-lattice relaxation rate were measured for the two crystallographically inequivalent Ga sites and for both Ga isotopes, in the temperature range 1.6 K - 300 K. No evidence of significant charge fluctuations is found from the NQR observables. On the contrary, the low-energy dynamics is dominated by anisotropic spin fluctuations with strong, nearly critical, in-plane character, which are effectively identical to the case of the sister compound PuCoIn${}_5$. These findings are discussed within the context of different theoretical proposals for the unconventional pairing mechanism in heavy-fermion superconductors.

arXiv comment7 pages, 8 figures

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Cited by in corpus (2)

• Orbital-dependent correlations in PuCoGa${}_5$
• Probing magnetism in the vortex phase of PuCoGa${}_5$ by X-ray magnetic circular dichroism