INELASTIC NEUTRON-SCATTERING IN SINGLE-CRYSTAL YBINCU4

We have measured the momentum and energy dependence of the spin fluctu ations in the low-temperature mixed-valent state and the high-temperat ure integral-valent state of YbInCu4, using flux-grown single crystals and a triple axis spectrometer. The magnetic scattering can be fit wi th a Lorentzian power spectrum, with positions and halfwidths equal E- 0(+) = 2.3 meV and Gamma(+) = 1.8 meV in the high-temperature state at 50 K and E-0(-) = 40.2 meV and Gamma(-) = 12.3 meV in the low-tempera ture state at 20 K. Within the experimental uncertainties, the line sh ape as a function of energy transfer (i.e., the power spectrum) does n ot depend on momentum transfer Q. The static susceptibility (X)(Q) is no more than 10% larger at the zone boundary than at zone center for t he [1,0,0] direction. The results compare reasonably well to the predi ctions of the Anderson impurity model and to earlier measurements on p olycrystalline samples.