Spin susceptibility in the superconducting state of the ferromagnetic superconductor UCoGe

Hattori, T.; Karube, Kosuke; Ihara, Yukitoshi; Ishida, K.; Deguchi, K.; Sato, Noriaki; Yamamura, Tomoo

doi:10.1103/physrevb.88.085127

Cited by 15 publications

(13 citation statements)

References 20 publications

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“…In a previous study [1], we reported that UTe 2 is classified as an unconventional superconductor because of the absence of a coherence peak just below T c ; moreover, the small decrease in the Knight shift when H b, which is much smaller than the expected decrease in a spinsinglet superconductor, is favorable for a spin-triplet scenario, because the large spin component remains in the SC state. Similar Knight-shift behaviors were also observed in UPt 3 [15,16] and UCoGe [17,18]. To ensure spin triplet superconductivity, it is important to identify the spin state of the SC state.…”

supporting

confidence: 60%

Anisotropic response of spin susceptibility in the superconducting state of UTe$_2$ probed with $^{125}$Te-NMR measurement

Nakamine,

Kinjo,

Kitagawa

et al. 2021

Preprint

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To investigate spin susceptibility in a superconducting (SC) state, we measured the 125 Te-nuclear magnetic resonance (NMR) Knight shifts at magnetic fields (H) up to 6.5 T along the b and c axes of single-crystal UTe2, a promising candidate for a spin-triplet superconductor. In the SC state, the Knight shifts along the b and c axes (K b and Kc, respectively) decreased slightly and the decrease in K b was almost constant up to 6.5 T. The reduction in Kc decreased with increasing H, and Kc was unchanged through the SC transition temperature at 5.5 T, excluding the possibility of spin-singlet pairing. Our results indicate that spin susceptibilities along the b and c axes slightly decrease in the SC state in low H, and the H response of SC spin susceptibility is anisotropic in the bc plane. We discuss the possible d-vector state within the spin-triplet scenario and suggest that the dominant d-vector component for the case of H b changes above 13 T, where Tc increases with increasing H.

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supporting

confidence: 60%

Anisotropic response of spin susceptibility in the superconducting state of UTe$_2$ probed with $^{125}$Te-NMR measurement

Nakamine,

Kinjo,

Kitagawa

et al. 2021

Preprint

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“…In this paper, in order to elucidate the origin of small δχ spin for magnetic fields parallel to the b-axis observed in the NMR Knight shift measurement of UTe 2 , 14) we numerically calculated the transverse spin susceptibility χ bb using the j = 5/2 multi-orbital model. As a result, the decrease in χ bb is sufficiently small for each d-vector candidate, implying that the band splitting due to the SO interaction can explain the results of the NMR Knight shift experiment 15) and the anomalously large upper critical field of UTe 2 for magnetic fields in the hard-axis direction.…”

Section: Discussionmentioning

confidence: 99%

“…In fact, the small δχ spin of UCoGe was experimentally verified via the NMR Knight shift measurements. 14) Thus, the anomalous behaviors of H c2 in the FM-SCs are explained by ferromagnetism. However, the same explanation is not applicable to UTe 2 , because it is paramagnetic.…”

Section: Introductionmentioning

confidence: 99%

Paramagnetic effects of j-electron superconductivity and application to UTe2

Hiranuma,

Fujimoto

2020

Preprint

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The putative spin-triplet superconductor UTe 2 has an Ising-like magnetic anisotropy, indicating the Cooper pair spins parallel to the easy-axis. However, the upper critical field for the hard-axis direction is much larger than that for the easy-axis, implying the strong suppression of the Pauli depairing effect even for the hard-axis direction. This observation is consistent with the recent NMR measurements which show the tiny decrease of the Knight shift below the transition temperature T c for hard-axis magnetic fields. We clarify that these behaviors are naturally understood as a result of multi-orbital f -electron bands with total angular momentum j = 5/2. Taking into account spin-orbit couplings for an orthorhombic structure, we demonstrate that for hard-axis magnetic fields, the decrease of the spin susceptibility below T c and the Pauli depairing effect are strongly suppressed.

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“…[14][15][16][17][18][19][20] In fact, the spin-triplet state with the spin component along the c-axis was suggested from the Knight-shift measurement in the field along the a-and b-axes. 21 Here, we discuss the similarity and difference in the SC enhancement observed between URhGe and UCoGe. Both compounds show the FM ordering with the Ising character along the c-axis (ordered moment: m c ∼ 0.40 µ B in URhGe and m c ∼ 0.05 µ B in UCoGe.…”

mentioning

confidence: 90%

Relationship between Ferromagnetic Criticality and the Enhancement of Superconductivity Induced by Transverse Magnetic Fields in UCoGe

et al. 2014

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We have performed 59 Co NMR experiments on the ferromagnetic superconductor UCoGe under magnetic fields (H) along the a-and b-axes to investigate the relationship between ferromagnetic properties and superconductivity. The ferromagnetic ordering temperature T Curie is suppressed and the nuclear spin-lattice relaxation rate 1/T 1 at 2 K is enhanced in H || b, although T Curie and 1/T 1 are unchanged in H || a, indicating that the ferromagnetic criticality is induced only when H is applied along the b axis. We show the close relationship between the magnetic anisotropies and the superconducting ones reported by Aoki et al.: the superconductivity is gradually suppressed in H || a, but enhanced in H || b above 5 T. We strongly suggest that the enhancement of the superconductivity observed in H || b originates from the field induced ferromagnetic criticality, as pointed out by Aoki et al and Mineev.UCoGe exhibits the ferromagnetic (FM) ordering at a low Curie temperature T Curie of ∼ 3 K and a superconducting (SC) transition temperature T SC of ∼ 0.8 K at ambient pressure, 1 which is the highest among the FM superconductors discovered so far. Although UCoGe possesses a three-dimensional crystal structure, its magnetic property is the Ising anisotropy with the c-axis being the easy axis.2, 3 In addition, its SC upper critical fields (H c2 ) also have strong anisotropy; superconductivity survives far beyond the Pauli-limiting field along the aand b-axes, whereas H c2 along the c-axis is as small as 0.5 T. 2, 3Since UCoGe includes the familiar NMR-active nucleus 59 Co, it is a suitable compound for NMR measurements within the FM superconductors. We have shown that superconductivity occurs in the FM region from the 59 Co nuclear quadrupole resonance (NQR), resulting in the microscopic coexistence of ferromagnetism and superconductivity. This is consistent with the µSR result.4 From the precise angleresolved NMR at 1.7 K and Meissner measurements at 85 mK, we show that the magnetic field along the c-axis strongly suppresses the Ising FM fluctuations along the c-axis and that the superconductivity is observed only in the limited magnetic field region where the FM spin fluctuations are active.5 These results, combined with model calculations, strongly suggest that the Ising FM spin fluctuations tuned by H || c induce the unique spin-triplet superconductivity by resolving the above puzzling H c2 behavior.Although the external magnetic field along the c-axis is the tuning parameter of the Ising FM fluctuations and the key to understanding the small H c2 along the c-axis, the magnetic field along the b-axis, which is the second magnetic easy axis and perpendicular to the U-U zigzag chain, also * E-mail: t.hattori@scphys.kyoto-u.ac.jp † E-mail: kishida@scphys.kyoto-u.ac.jp tunes the superconductivity. 3 The superconductivity becomes robust against the external field along the b axis when µ 0 H greater than 5 T is applied, which is reminiscent of the reentrant superconductivity in the sister compound URhGe, 6,7 as discussed l...

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Spin susceptibility in the superconducting state of the ferromagnetic superconductor UCoGe

Cited by 15 publications

References 20 publications

Anisotropic response of spin susceptibility in the superconducting state of UTe$_2$ probed with $^{125}$Te-NMR measurement

Anisotropic response of spin susceptibility in the superconducting state of UTe$_2$ probed with $^{125}$Te-NMR measurement

Paramagnetic effects of j-electron superconductivity and application to UTe2

Relationship between Ferromagnetic Criticality and the Enhancement of Superconductivity Induced by Transverse Magnetic Fields in UCoGe

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