Pseudogap and Incommensurate Magnetic Fluctuations in YBa₂Cu₃O₆.₆

Unpolarized inelastic neutron scattering is used to study the temperature and wave vector dependence of the dynamical magnetic susceptibility, Χ (q, ω), of a well-characterized single-crystal YBa2Cu3O6.6 (Tc = 62.7 K). We find that a pseudogap opens in the spin-fluctuation spectrum at temperatures well above Tc. We speculate that the appearance of the low-frequency incommensurate fluctuations is 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 superconducting state