CU-63 KNIGHT-SHIFT STUDY IN HIGH-TC SUPERCONDUCTOR TL2BA2CUO6+Y WITH A SINGLE CUO2 LAYER

63Cu Knight shift in Tl2Ba2CuO6+y, with a single CuO2 plane has been measured by using a partially oriented powder with the c-axis perpendicular to the external field (Kab). For the compounds with Tc=72 K and 40 K, Kab exclusively connected to the spin susceptibility (χs) is T-independent above Tc, while it decreases rapidly below Tc. By taking into account the T-independent orbital shift of Korb = 0.24% and 0.26%, respectively, χs(T) is found to become almost zero below T/Tc = 0.3, in good agreemt with the isotropic energy gap (s-wave) model with a larger energy gap (2Δ=4.4kBTc) than the BCS value (2Δ=3.5kBTc). For the nonsuperconducting Tl2Ba2CuO6+y Kab(χs) exhibits no T-variation, which is different from the behavior observed in other high-Tc oxides except YBa2Cu3O7. © 1990, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.