Pairing mechanism in the ferromagnetic superconductor UCoGe

Wu, Beilun; Bastien, Gäel; Taupin, Mathieu; Paulsen, C.; Howald, Ludovic; Aoki, Dai; Brison, Jean-Pascal

doi:10.1038/ncomms14480

Cited by 64 publications

(76 citation statements)

References 46 publications

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“…For UCoGe, it was reported from a field-angle-controlled nuclear magnetic resonance (NMR) experiment that the Ising-type FM fluctuations along the c axis are essential for the pairing 12 . The changes in pairing strength with the fields were quantitatively analyzed by measuring the upper critical field H c2 , and this result supports the scenario of FM fluctuation-mediated superconductivity 13 . FM fluctuations also play an important role in superconductivity in URhGe; however, transverse fluctuations as well as those parallel to the c axis were also found to contribute to the pairing 14 .…”

Section: Introductionsupporting

confidence: 64%

Spin-triplet superconductivity in the paramagnetic UCoGe under pressure studied by Co59 NMR

et al. 2019

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A 59 Co nuclear magnetic resonance (NMR) measurement was performed on the single-crystalline ferromagnetic (FM) superconductor UCoGe under a pressure of 1.09 GPa, where the FM state is suppressed and superconductivity occurs in the paramagnetic (PM) state, to study the superconducting (SC) state in the PM state. 59 Co-NMR spectra became broader but hardly shifted across the SC transition temperature. The Knight-shift change determined from fitting the spectral peak with a Gaussian was much smaller than the spin part of the Knight shift; this is in good agreement with the spin-triplet pairing suggested from the large upper critical field. The spectrum broadening in the SC state cannot be attributed to the SC diamagnetic effect, but is related to the properties of spin-triplet superconductivity. The origins of the broadening are discussed herein.

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Section: Introductionsupporting

confidence: 64%

Spin-triplet superconductivity in the paramagnetic UCoGe under pressure studied by Co59 NMR

et al. 2019

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“…2(b) in Ref. 35). According to NMR by Manago et al 25 , 1/T T 1 shows very similar behaviors: plateau at N (0)/2 and sudden drop mentioned above.…”

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confidence: 91%

Theory of Spin-polarized Superconductors —An Analogue of Superfluid ³He A-phase—

Machida

2020

J. Phys. Soc. Jpn.

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It is shown theoretically that ferromagnetic superconductors, UGe2, URhGe, and UCoGe can be described in terms of the A-phase like triplet pairing similar to superfluid 3 He in a unified way, including peculiar reentrant, S-shape, or L-shape Hc2 curves. The associated double transition inevitable between the A1 and A2-phases in the H-T plane is predicted, both of which are characterized by non-unitary state with broken time reversal symmetry and the half-gap. UTe2, which has been discovered quite recently to be a spin-polarized superconductor, is analyzed successively in the same view point, pointing out that the expected A1-A2 transition is indeed emerging experimentally. Thus the four heavy Fermion compounds all together are entitled to be topologically rich solid state materials worth further investigating together with superfluid 3 He A-phase.

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“…Other parameters like the screened Coulomb potential µ* are governed by large energy scales and logarithmic cut-off, so they are expected to change very little in the small stress of field range applied. Using a minimal strong coupling model [19] to calculate the T SC dependence on λ and the corresponding H c2 , (taking the dependence of the Fermi velocity into account), we could extract, as explained in reference [9] how λ should vary under stress and field, once the value for λ (H=0, σ =0) is properly chosen.…”

Section: Magnetization Measurements Under Stressmentioning

confidence: 99%

“…The direct coupling between a static uniform field and ferromagnetism also leads to fascinating behaviour of the superconducting state under magnetic field. In these systems the pairing mechanism can actually be tuned by magnetic field, either increased [7,8] or suppressed [9], respectively when the magnetic field is applied perpendicular to (transverse field configuration) or along (longitudinal configuration) the easy magnetization axis. The most striking case is URhGe.…”

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confidence: 99%

“…Of course as H R decreases, the maximum T SC HR occurs at a lower field, so the orbital pair-breaking effect of the field is weaker and will naturally lead to a higher T SC . To eliminate the influence of the reduced orbital effect when H R occurs at lower field, and better quantify the reinforcement of superconductivity, we have analysed the superconducting upper critical field (H C2 ) curves using a strong-coupling model [19], following the approach developed in Wu et al [9]. The hypothesis is that all changes of T SC and of the effective mass figure 5b, the enhancement of λ between zero field and H R, plotted versus H/H R , appears to be independent of stress.…”

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confidence: 99%

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Dimensionality Driven Enhancement of Ferromagnetic Superconductivity in URhGe

et al. 2018

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In most unconventional superconductors, like the high-T c cuprates, iron pnictides, or heavy fermion systems, superconductivity emerges in the proximity of an electronic instability. Identifying unambiguously the pairing mechanism remains nevertheless an enormous challenge. Among these systems, the orthorhombic uranium ferromagnetic superconductors have a unique position, notably because magnetic fields couple directly to ferromagnetic order, leading to the fascinating discovery of the re-emergence of superconductivity in URhGe at high field. Here we show that uniaxial stress is a remarkable tool allowing fine-tuning of the pairing strength.With a relatively small stress, the superconducting phase diagram is spectacularly modified, with a merging of the low and high field superconducting states and a significant enhancement of superconductivity. The superconducting critical temperature increases both at zero field and under field, reaching 1K, more than twice higher than at ambient pressure. The enhancement of superconductivity is directly related to a change of the magnetic dimensionality with an increase of the transverse magnetic susceptibility, demonstrating that in addition to the Ising-type longitudinal ferromagnetic fluctuations, transverse magnetic fluctuations also play an important role in the superconducting pairing.For usual s-wave superconductors, superconductivity and ferromagnetism are antagonist states as the ferromagnetic exchange field easily destroys the superconducting pairs.Therefore the discovery of the microscopic co-existence of superconductivity and ferromagnetism in three orthorhombic uranium based heavy-fermion systems (UGe 2 , URhGe, UCoGe)[1-6] was one of the most exciting events in recent condensed matter physics. This coexistence strongly suggests a superconducting state with triplet pairing, where the Pauli limiting mechanism is not active and the Cooper pairs can survive in the strong exchange field. The direct coupling between a static uniform field and ferromagnetism also leads to fascinating behaviour of the superconducting state under magnetic field. In these systems the pairing mechanism can actually be tuned by magnetic field, either increased [7,8] or

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Pairing mechanism in the ferromagnetic superconductor UCoGe

Cited by 64 publications

References 46 publications

Spin-triplet superconductivity in the paramagnetic UCoGe under pressure studied by Co59 NMR

Spin-triplet superconductivity in the paramagnetic UCoGe under pressure studied by Co59 NMR

Theory of Spin-polarized Superconductors —An Analogue of Superfluid ³He A-phase—

Dimensionality Driven Enhancement of Ferromagnetic Superconductivity in URhGe

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Pairing mechanism in the ferromagnetic superconductor UCoGe

Cited by 64 publications

References 46 publications

Spin-triplet superconductivity in the paramagnetic UCoGe under pressure studied by Co59 NMR

Spin-triplet superconductivity in the paramagnetic UCoGe under pressure studied by Co59 NMR

Theory of Spin-polarized Superconductors —An Analogue of Superfluid 3He A-phase—

Dimensionality Driven Enhancement of Ferromagnetic Superconductivity in URhGe

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Theory of Spin-polarized Superconductors —An Analogue of Superfluid ³He A-phase—