⁵⁹Co-NMR Knight Shift of Aligned Crystals and Polycrystalline Samples of Superconducting Na_0.3CoO₂·1.3H₂O

Abstract

Temperature (T) dependence of 59Co-NMR Knight shifts K of Na0.3CoO2.1.3H2O\nhas been studied, where samples of randomly oriented powder and aligned\ncrystals have been used for the applied magnetic fields H // ab plane and H\n//c-axis, respectively. For both directions of H, the shift K decreases below\nthe superconducting transition temperature Tc(H) with decreasing T, indicating\nthat the superconducting electron pairs are in the singlet state. The upper\ncritical fields Hc2(T) determined from the K(H)-T curves are found to be\nconsistent with the values reported by the resistivity measurements for both\ndirections of H.\n