Pseudogap and incommensurate magnetic fluctuations in YBazCu3O6.6

Unpolarized inelastic neutron scattering is used to study the temperature and wave vector dependence of the dynamical magnetic susceptibility, ~"(q, ~), of a well-characterized single-crystal YBa2Cu30~.6 (T c = 62.7 K). We find that a pseudogap opens in the spin-fluctuation spectrum at temperatures well above T c. We speculate that the appearance of the low-frequency incommensurate fluctuations i associated with the opening of the pseudogap. To within the error of the measurements, a gap in the spin-fluctuation spectrum is found in the superconductin