PSEUDOGAP AND INCOMMENSURATE MAGNETIC FLUCTUATIONS IN YBA2CU3O6.6

Unpolarized inelastic neutron scattering is used to study the temperat ure and wave vector dependence of the dynamical magnetic susceptibilit y, chi ''(q, omega), of a well-characterized single-crystal YBa2Cu3O6. 6 (T-c = 62.7 K). We find that a pseudogap opens in the spin-fluctuati on spectrum at temperatures well above T-c. We speculate that the appe arance of the low-frequency incommensurate fluctuations is associated with the opening of the pseudogap. To within the error of the measurem ents, a gap in the spin-fluctuation spectrum is found in the supercond ucting state. (C) 1998 Published by Elsevier Science B.V. All rights r eserved.