NMR study of magnetic excitations and pseudogap in HgBa2Ca3Cu4Oy

We report systematic Cu-NMR study on HgBa2Ca3Cu4O10+y with T-c = 123 K comp rising respective 4-fold and 5-fold two CuO2 planes surrounded by square an d pyramidal oxygens. Possible structure and temperature dependence of the n ormal-state pseudogap have been extracted from the steep decrease of the sp in contribution in the Knight shift, K-s below T-K*similar to 220K. By assu ming the linear increase of a size of pseudogap between T-K* and T-c with t he d(x2-y2) symmetry, the T-dependence of K-s/K-n in both 4- and 5-fold is reproduced below T-K*. (C) 1999 Elsevier Science B.V. All rights reserved.