Detection of a Spin-Triplet Superconducting Phase in Oriented PolycrystallineU2PtC2Samples Using

Abstract

Nuclear magnetic resonance (NMR) measurements on the 195 Pt nucleus in an aligned powder of the moderately heavy-fermion material U2PtC2 are consistent with spin-triplet pairing in its superconducting state. Across the superconducting transition temperature and to much lower temperatures, the NMR Knight shift is temperature independent for field both parallel and perpendicular to the tetragonal c-axis, expected for triplet equal-spin pairing superconductivity. The NMR spin-lattice relaxation rate 1/T1, in the normal state, exhibits characteristics of ferromagnetic fluctuations, compatible with an enhanced Wilson ratio. In the superconducting state, 1/T1 follows a power law with temperature without a coherence peak giving additional support that U2PtC2 is an unconventional superconductor. Bulk measurements of the AC-susceptibility and resistivity indicate that the upper critical field exceeds the Pauli limiting field for spin-singlet pairing and is near the orbital limiting field, an additional indication for spin-triplet pairing.

Thermal and transport properties of U2PtxIr1–xC2

“…Thus, this is consistent with non-magnetic scattering suppressing superconductivity in an unconventional superconductor. These observations are consistent with NMR and upper critical field measurements, which indicate that U 2 PtC 2 is a spin-triplet superconductor [10]. In Rh doped U 2 PtC 2 superconductivity is slightly more robust, extending to x = 0.8, while the scattering rate increases more quickly relative to Ir doping, leading to a mild violation of the theory of Abrikosov and Gorkov applied to unconventional superconductors.…”

“…Recent nuclear magnetic resonance (NMR) measurements indicate that U 2 PtC 2 is a spin triplet superconductor with strong ferromagnetic electronic correlations [10]. The normal state is found to be a moderately mass enhanced Fermi liquid with a Sommerfeld coefficient of γ = 75 mJ mol −1 K −2 [6].…”

Magnetism and superconductivity inU2PtxRh1−xC2

“…This suggests that perhaps the antiferromagnetic quantum fluctuations do not enhance the superconducting pairing. Indeed, recent NMR measurements in U 2 PtC 2 have shown evidence for unconventional superconductivity and more specifically spin-triplet pairing 9 . Hence, the nature of the superconducting state requires closer investigation.…”

“…The mechanism for superconductivity in U 2 PtC 2 is an open question. Recent nuclear magnetic resonance (NMR) measurements of U 2 PtC 2 have shown evidence for spin triplet pairing and unconventional superconductivity 9 . Isostructural U 2 RhC 2 displays no superconductivity but orders antiferromagnetically at a Néel temperature T N ∼ 22 K, and shows evidence for possible "complex magnetic behaviour" at lower temperatures 8 .…”