HG-199 AND CU-63 NMR IN SUPERCONDUCTING HGBA2CUO4+DELTA ORIENTED POWDER

Hg-199 NMR measurements have been performed both in the normal and in the superconducting state for an oriented HgBa2CuO4+delta superconduct ing powder sample with T-c = 96 K. The large anisotropic Knight shift of Hg-199, K-199(ax) = -0.15% at room temperature, is explained by the chemical shift related to the linear Hg-O(2) bonding configuration. B oth K-199(iso) and K-199(ax) decrease below T-c and scale linearly wit h each other in the whole temperature range investigated. The Hg-199 K night shift K-199 slowly decreases with decreasing temperature on appr oaching T-c in the normal state, reflecting the decrease of the unifor m spin susceptibility chi '(0,0) with lowering temperature. The Hg-199 spin-echo decay can be fit by the product of a Gaussian component T-G (-1) and an exponential one (T-L(-1)). The Gaussian component T-G(-1) which is dominant above T-c, is shown to be due mainly to an indirect nuclear interaction via the conduction electrons (holes) and is found to be directly proportional to the spin contribution (K-199(sp)) of th e Knight shift. The exponential component T-L(-1) becomes dominant wel l below T-c and is ascribed to the effect of thermal motion of flux li nes. The Hg-199 nuclear spin-lattice relaxation rate T-1(-1) in the no rmal state shows a Korringa behavior well above T-c with (T1T)(-1) = 0 .1 sec(-1) K-1. Reduction of (T1T)(-1) with decreasing temperature is observed starting about 10 K above T-1 and is consistent with the decr ease of chi '(0,0) in the normal state observed in K(T) and T-G(-1) K- 199(sp)(T) was extracted using the Korringa relation and below T-c, is found to fit the d-wave pairing scheme with a superconducting gap par ameter 2 Delta(0)=3.5k(B)T(c). The d-wave pairing is also supported by the temperature dependence of Hg-199 T-1(-1) in the superconducting s tate. The (CU)-C-63 T-1(-1) and T-2(-1) measurements have been perform ed in the normal state. In contrast to the Korringa behavior of Hg-199 T-1(-1) in the normal state, the preliminary results show the increas e of the (63) Cu (T1T)(-1) with decreasing temperature, indicating the enhancement of the antiferromagnetic fluctuations of CU2+ moments com mon in the high-T-c cuprates. The reduction of (CU)-C-63 (T1T)(-1) is observed starting above T-c and is compared with the decrease of Hg-19 9 K-sp, T-G(-1), and (T1T)(-1) in the normal state. The (CU)-C-63 nucl ear spin-spin relaxation T-2(-1) is found to follow an exponential dec ay in the normal state and to decrease with decreasing temperature sim ilar to the Hg-199 K-sp and T-G(-1).