⁵⁹Co-NMR Knight Shift of Superconducting Na_xCoO₂·yH₂O

Abstract

Layered Co oxide Na x CoO 2 ÁyH 2 O with the superconducting transition temperature T c ¼ 4:5 K has been studied by 59 Co-NMR. The Knight shift K estimated from the observed spectra of a powder sample exhibits almost temperature (T)-independent behavior above T c and decreases with decreasing T below T c . This result and the existence of the coherence peak in the spin-lattice relaxation rate versus T curve reported by the present authors indicate, naively speaking, that the singlet order parameter with s-wave symmetry is realized in Na x CoO 2 ÁyH 2 O. Differences in the observed behaviors between the spectra of a nonaligned sample and those of an aligned sample embedded in epoxy adhesive by applying an external magnetic field are discussed.

Nesting, Spin Fluctuations, and Odd-Gap Superconductivity inNaxCoO2·yJohannes1, Mazin2, Singh3 et al. 2004Phys. Rev. Lett.812131View full textAdd to dashboardCite

“…In most experiments such a peak is not observed, but a rather weak coherence peak was seen in Ref. [15,18]. Third, specifically the d ẑ triplet s-state, similar to the chiral p-state in Sr 2 RuO 4 , implies no change in the in-plane susceptibility, as measured by the Knight shift.…”

Study of the triangular latticetVmodel nearx=13

“…The experimental situation regarding the pairing symmetry of Na x CoO 2 · yH 2 O remains inconclusive, with controversy still surrounding whether there is a jump in the Knight shift below T c . 15,16 …”

A critical assessment of the superconducting pairing symmetry in NaxCoO2·yH2O

“…The orbital angular momentum, L , of each state is labelled in the rightmost column and conformity/non-conformity with each of our three criteria is indicated by Y/N (for yes/no) in the remaining three columns. for Na x CoO 2 ·yH 2 O have measured the temperature dependence of either specific heat 23,24 or relaxation rates (nuclear magnetic resonance 5 , nuclear quadrupole resonance 25,26 and muon spin relaxation, μSR 3,27 ). In all of these works, the authors agree that the low-temperature behaviour of the DOS is not exponential, indicating the absence of a full gap.…”

“…Finally, we would like to comment on the (still controversial) Knight shift experiments [2][3][4][5] . The f -wave states that have emerged from our discussion correspond to Cooper pairs with spins in the xy plane and thus to a constant Knight shift.…”