Extended nuclear quadrupole resonance study of the heavy-fermion superconductor<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="bold">PuCoGa</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:math>

Koutroulakis, G.; Yaśuoka, Hiroshi; Tobash, Paul H.; Mitchell, Jeanette; Bauer, E. D.; Thompson, J. D.

doi:10.1103/physrevb.94.165115

Cited by 5 publications

(3 citation statements)

References 38 publications

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“…These results have been interpreted as evidence for a valence transition at a T V < T c that is avoided by the superconducting state [14]. On the other hand, the relaxation rate isotope ratio T [15] that could, nevertheless, be associated with charge (valence) fluctuations with a higher energy scale. High-resolution powder x-ray-diffraction recently showed that the volume expansion of PuCoGa 5 deviates from the curve expected for a simple Grüneisen-Einstein model, but the observed variations are too small to be taken as an indication for the proximity of the system to a valence instability [16].…”

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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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confidence: 90%

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

et al. 2017

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“…Beyond characterizing QN spin systems, NQR spectroscopy has proven its scientific versatility in several applications and studies as, for example, research on molecular structure [66,67], superconductors [68], semiconductors [69], and phase transitions [70,71], as well as quantum computing [72] and the authentication of medicines [73].…”

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confidence: 99%

Tuning Nuclear Quadrupole Resonance: A Novel Approach for the Design of Frequency-Selective MRI Contrast Agents

et al. 2018

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The interaction between water protons and suitable quadrupolar nuclei (QN) can lead to quadrupole relaxation enhancement (QRE) of proton spins, provided the resonance condition between both spin transitions is fulfilled. This effect could be utilized as a frequency selective mechanism in novel, responsive T 1 shortening contrast agents (CAs) for magnetic resonance imaging (MRI). In particular, the proposed contrast mechanism depends on the applied external flux density-a property that can be exploited by special field-cycling MRI scanners. For the design of efficient CA molecules, exhibiting narrow and pronounced peaks in the proton T 1 relaxation dispersion, the nuclear quadrupole resonance (NQR) properties, as well as the spin dynamics of the system QN-1 H, have to be well understood and characterized for the compounds in question. In particular, the energy-level structure of the QN is a central determinant for the static flux densities at which the contrast enhancement appears. The energy levels depend both on the QN and the electronic environment, i.e., the chemical bonding structure in the CA molecule. In this work, the NQR properties of a family of promising organometallic compounds containing 209 Bi as QN have been characterized. Important factors like temperature, chemical structure, and chemical environment have been considered by NQR spectroscopy and ab initio quantum chemistry calculations. The investigated Bi-aryl compounds turned out to fulfill several crucial requirements: NQR transition frequency range applicable to clinical 1.5-and 3 T MRI systems, low temperature dependency, low toxicity, and tunability in frequency by chemical modification.

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“…In fact, a comparison between the properties of PuCoGa 5 and PuCoIn 5 has suggested two distinct electron pairing mechanisms, one due to spin fluctuations and the other mediated by valence fluctuations. 11,12 Although the electron pairing mechanism is still under debate, more recent experiments clearly evidence a d-wave superconductivity in PuCoGa 5 . 13 Early theoretical works employed different methods to study the electronic structure of PuCoGa 5 .…”

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confidence: 99%

Orbital-dependent correlations in PuCoGa5

et al. 2018

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We investigate the normal state of the superconducting compound PuCoGa5 using the combination of density functional theory (DFT) and dynamical mean field theory (DMFT), with the continuous time quantum Monte Carlo (CTQMC) and the vertex-corrected one-crossing approximation (OCA) as the impurity solvers. Our DFT+DMFT(CTQMC) calculations suggest a strong tendency of Pu-5f orbitals to differentiate at low temperatures. The renormalized 5f 5/2 states exhibit a Fermi-liquid behavior whereas one electron in the 5f 7/2 states is at the edge of a Mott localization. We find that the orbital differentiation is manifested as the removing of 5f 7/2 spectral weight from the Fermi level relative to DFT. We corroborate these conclusions with DFT+DMFT(OCA) calculations which demonstrate that 5f 5/2 electrons have a much larger Kondo scale than the 5f 7/2 .

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Extended nuclear quadrupole resonance study of the heavy-fermion superconductorPuCoGa5

Cited by 5 publications

References 38 publications

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

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

Tuning Nuclear Quadrupole Resonance: A Novel Approach for the Design of Frequency-Selective MRI Contrast Agents

Orbital-dependent correlations in PuCoGa5

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