NMR Study of High-Tc Superconductors
Cu NQR and oxygen NMR studies of high Tc materials are reported. The behavior of the Cu nuclear spin-lattice relaxation in CuO2 planer site is demonstrated to be unconventional above and below Tc for (La0.925Sr0.075)2CuO4 (Tc=38 K), YBa2Cu3O7 (Tc=92K) and Bi-Pb-Sr-Ca-Cu-O (Tc=109 K) compared with BCS superconductor. From the hole content dependence of T1 in (La1−xSrx)2CuO4, the normal state of high Tc materials is found to be dominated by the antiferromagnetic spin fluctuations. The Knight shift of 17O has been measured for the 0O(1) site in CuO2 plane and O(2) site in the Lao layer in (C.a0.925Sr0.075)2CuO4. In normal state, the shift for the O(1) site decreases with decreasing temperature in proportion to the bulk susceptibility, while the shift for O(2) site is temperature independent. Below Tc, both shifts decrease with a moderate rate compared to the shift for O(2,3) site in YBa2Cu3O7 which shows a faster reduction than the BCS prediction. The coupling between the localized spins at Cu(2) sites and the mobile oxygen p-holes is discussed in the light of these results.
KeywordsSpin Correlation Spin Fluctuation Knight Shift Oxygen Site Nuclear Spin Lattice Relaxation Rate
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