Strong-coupling d-wave superconductivity in PuCoGa5 probed by point-contact spectroscopy

Daghero, Dario; Tortello, Mauro; Ummarino, Giovanni; Griveau, Jean‐Christophe; Colineau, E.; Eloirdi, R.; Shick, A. B.; Kolorenč, Jindřich; Lichtenstein, A. I.; Caciuffo, R.

doi:10.1038/ncomms1785

Cited by 58 publications

(63 citation statements)

References 54 publications

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“…The results indicate an occupation number of the Pu 5f shell very close to 5, corresponding to a stable Pu 3+ configuration, in contrast to δ-Pu and PuCoGa 5 for which an intermediate valence configuration has been suggested. 22 The high temperature anomalies that are always present in the parent RFeAsO compounds are not observed in PuFeAsO, and so we would suggest that, similar to NpFeAsO, spin density wave condensation and structural phase transition are not present in PuFeAsO. Continuing the trend from Np to Pu and on to Am, one might imagine that the increased degree of localization of the Am 5f electrons might be more compatible with a magnetic structure on the iron independent of that on the f electron ion, such that the SDW and related structural transition might be present.…”

Section: Discussionmentioning

confidence: 99%

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Bulk properties and electronic structure of PuFeAsO

et al. 2012

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Here we present bulk property measurements and electronic structure calculations for PuFeAsO, an actinide analog of the iron-based rare-earth superconductors RFeAsO. Magnetic susceptibility and heat capacity data suggest the occurrence of an antiferromagnetic transition at T N = 50 K. No further anomalies have been observed down to 2 K, the minimum temperature that we have been able to achieve. Structural measurements indicate that PuFeAsO, with its more localized 5f electrons, bears a stronger resemblance to the RFeAsO compounds with larger R ions than NpFeAsO does.

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Section: Discussionmentioning

confidence: 99%

“…A similar calculation performed for the PuCoGa 5 superconductor yields n f = 5.30 and n f + n bath = 14, corresponding to a singlet ground state for the composite cluster. 22 This suggests that the f electrons in PuFeAsO are less hybridized with the conduction band than in PuCoGa 5 and are close to a static integer valence.…”

Section: Mj Kmentioning

confidence: 99%

Bulk properties and electronic structure of PuFeAsO

et al. 2012

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“…Further arguments in favor of SFs-controlled SC were provided by NMR studies [2], revealing a nodal-gap function separating the condensate from the unpaired states. Subsequent point-contact spectroscopy measurements confirmed that the wavefunction of the paired electrons has an unconventional d-wave symmetry [3]. However, the SF conjecture was questioned [4,5] after polarized neutron diffraction failed to observe a local magnetic moment in the normal state of PuCoGa 5 [6], pointing to an extrinsic origin of the reported temperature dependent χ m .…”

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Probing Magnetism in the Vortex Phase of PuCoGa5 by X-Ray Magnetic Circular Dichroism

et al. 2017

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We have measured X-ray magnetic circular dichroism (XMCD) spectra at the Pu M4,5 absorption edges from a newly-prepared high-quality single crystal of the heavy fermion superconductor 242 PuCoGa5, exhibiting a critical temperature Tc = 18.7 K. The experiment probes the vortex phase below Tc and shows that an external magnetic field induces a Pu 5f magnetic moment at 2 K equal to the temperature-independent moment measured in the normal phase up to 300 K by a SQUID device. This observation is in agreement with theoretical models claiming that the Pu atoms in PuCoGa5 have a nonmagnetic singlet ground state resulting from the hybridization of the conduction electrons with the intermediate-valence 5f electronic shell. Unexpectedly, XMCD spectra show that the orbital component of the 5f magnetic moment increases significantly between 30 and 2 K; the antiparallel spin component increases as well, leaving the total moment practically constant. We suggest that this indicates a low-temperature breakdown of the complete Kondo-like screening of the local 5f moment.PuCoGa 5 is a prototypical heavy-fermion compound that becomes a superconductor below T c ≃ 18.5 K [1], the highest critical temperature of any heavy-fermion material. Fifteen years on its discovery, the nature of the pairing boson in PuCoGa 5 remains an open question. Superconductivity (SC) mediated by spin fluctuations (SFs) associated with the proximity to an antiferromagnetic (AFM) quantum critical point (QCP) was initially proposed. The hypothesis was supported by the observation in the normal phase of a Curie-Weiss (CW) behavior of the magnetic susceptibility χ m , suggesting the presence of Pu atoms carrying a local magnetic moment. Further arguments in favor of SFs-controlled SC were provided by NMR studies [2], revealing a nodal-gap function separating the condensate from the unpaired states. Subsequent point-contact spectroscopy measurements confirmed that the wavefunction of the paired electrons has an unconventional d-wave symmetry [3]. However, the SF conjecture was questioned [4,5] after polarized neutron diffraction failed to observe a local magnetic moment in the normal state of PuCoGa 5 [6], pointing to an extrinsic origin of the reported temperature dependent χ m . This observation is confirmed in the present article by showing that the magnetic susceptibility of an almost defect-free PuCoGa 5 single crystal is weak and temperature-independent from T c up to room temperature.Other members of the PuM X 5 family (M = Co, Rh, and X = Ga, In) also become superconductors, with T c ranging from ∼1.7 K in the case of PuRhIn 5 to ∼8.7 K for PuRhGa 5 [7]. The much larger T c of PuCoGa 5 could indicate that a different pairing mechanism is acting in the various compounds of the family. Indeed, Bauer et al.[8] proposed that SC in PuCoIn 5 (T c = 2.5 K) is related to an AFM QCP, whereas PuCoGa 5 would reside on a larger SC dome in the temperature-pressure (hybridization strength) phase diagram, around a valence fluctuation (VF) QCP. The hypothesis is suppor...

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“…Fifteen years after its discovery [1] our understanding of much of this material remains at best confused [2][3][4][5][6][7][8]. We do know from NMR [2] and point-contact spectroscopy [6] measurements that the superconducting state has d-wave symmetry. Magnetic form-factor measurements with polarized neutron diffraction [5] have shown that the ground state is not the conventional 5f…”

Section: Introductionmentioning

confidence: 99%

Thermal expansion of the heavy-fermion superconductor PuCoGa5

Eloirdi¹,

Giacobbe²,

Celdran³

et al. 2017

Phys. Rev. B

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We have performed high-resolution powder x-ray diffraction measurements on a sample of 242 PuCoGa5, the heavy-fermion superconductor with the highest critical temperature Tc = 18.7 K. The results show that the tetragonal symmetry of its crystallographic lattice is preserved down to 2 K. Marginal evidence is obtained for an anomalous behaviour below Tc of the a and c lattice parameters. The observed thermal expansion is isotropic down to 150 K, and becomes anisotropic for lower temperatures. This gives a c/a ratio that decreases with increasing temperature to become almost constant above ∼150 K. The volume thermal expansion coefficient αV has a jump at Tc, a factor ∼20 larger than the change predicted by the Ehrenfest relation for a second order phase transition. The volume expansion deviates from the curve expected for the conventional anharmonic behaviour described by a simple Grüneisen-Einstein model. The observed differences are about ten times larger than the statistical error bars but are too small to be taken as an indication for the proximity of the system to a valence instability that is avoided by the superconducting state.PACS numbers:

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Strong-coupling d-wave superconductivity in PuCoGa5 probed by point-contact spectroscopy

Cited by 58 publications

References 54 publications

Bulk properties and electronic structure of PuFeAsO

Bulk properties and electronic structure of PuFeAsO

Probing Magnetism in the Vortex Phase of PuCoGa5 by X-Ray Magnetic Circular Dichroism

Thermal expansion of the heavy-fermion superconductor PuCoGa5

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