59Co-NMR Knight Shift of Aligned Crystals and Polycrystalline Samples of Superconducting Na0.3CoO2.1.3H2O

摘要

Temperature (T) dependence of 59Co-NMR Knight shifts K of Na0.3CoO2.1.3H2Ohas been studied, where samples of randomly oriented powder and alignedcrystals have been used for the applied magnetic fields H // ab plane and H//c-axis, respectively. For both directions of H, the shift K decreases belowthe superconducting transition temperature Tc(H) with decreasing T, indicatingthat the superconducting electron pairs are in the singlet state. The uppercritical fields Hc2(T) determined from the K(H)-T curves are found to beconsistent with the values reported by the resistivity measurements for bothdirections of H.