Possible Spin-triplet Superconductivity in NaxCoO2yH2O - 59Co NMR Study

Abstract

We report 59Co NMR studies on the magnetically oriented powder samples of Co-oxide superconductors NaxCoO2yH2O with Tc ~ 4.7 K. From two-dimensional powder pattern in the NMR spectrum, the ab-plane Knight shift in the normal state was estimated by the magnetic field dependence of second-order quadrupole shifts at various temperatures. Below 50 K, the Knight shift shows a Curie-Weiss-like temperature dependence, similarly to the bulk magnetic susceptibility chi. From the analysis of so-called K-chi plot, the spin and the orbital components of K and the positive hyperfine coupling constant were estimated. The onset temperature of superconducting transition in the Knight shift does not change so much in an applied magnetic field up to 7 T, which is consistent with the reported high upper critical field Hc2. The Knight shift at 7 T shows an invariant behavior below Tc. No coherence peak just below Tc was observed in the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1 in both cases of NMR and NQR. We conclude that the invariant behavior of the Knight shift below Tc and unconventional behaviors of 1/T possibly indicate the spin-triplet superconductivity with p- or f-wave symmetry.

17 pages, 10 figures. Extended version

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Cited by in corpus (15)

• Nodal Structure of Unconventional Superconductors Probed by the Angle Resolved Thermal Transport Measurements
• Spin singlet pairing in the superconducting state of NaxCoO2\cdot1.3H2O: evidence from a ^{59}Co Knight shift in a single crystal
• Nodal $d+id$ pairing and topological phases on the triangular lattice: unconventional superconducting state of Na${}_x$CoO${}_2\cdot y$H${}_2$O
• 59Co Nuclear Quadrupole Resonance Studies of Superconducting and Non-superconducting Bilayer Water Intercalated Sodium Cobalt Oxides NaxCoO2.yH2O
• Spin gaps and magnetic structure of NaxCoO2
• Unconventional Superconductivity arising from Multipolar Kondo Interactions
• Electron-phonon interaction dressed by electronic correlations near charge ordering as the origin for superconductivity in cobaltates
• Small $T_1^{-1}$ coherence peak near $T_c$ in unconventional superconductors
• Identifying the pairing symmetry in sodium cobalt oxide by Andreev edge states
• 59Co, 23Na, and 1H NMR Studies of Double-Layer Hydrated Superconductors NaxCoO2-yH2O
• Doping dependence of Meissner effect in triangular-lattice superconductors
• One-particle spectral properties of the t-J-$V$ model on the triangular lattice near charge order
• Towards a Microscopic Theory of the Knight Shift in an Anisotropic, Multiband Type-II Superconductor
• Magnetic anomalies of hydrous cobaltate compound Na_x(H_3O)_zCoO_2 \cdot yH_2O detected by NMR and NQR measurements
• In-plane Anisotropy of the Magnetic Fluctuations in NaxCoO2-yH2O