No abstract

The spin dynamics of the underdoped superconductor YBa 2 Cu 3 O 6.7 (T c ϳ 67 K) was revealed to have an incommensurate wave vector dependence with "pillars" in the dispersion relation at the positions ( 1 2 6 d, 1 2 , 0) and ( 1 2 , 1 2 6 d, 0). This is the same symmetry as that found in La 22x Sr x CuO 4 . The value of the incommensurability, d 0.11 6 0.01 r.l.u ϳ 1 8 , is very close to the value expected from the hole concentration. These results have demonstrated that the spin dynamics do not depend on the details of Fermi surface but have an analogous form to that for the proposed stripe domain structure.

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Vibrational spectroscopy with inelastic neutron scattering can provide spectra that are more detailed and easier to interpret than optical spectra. The spectral intensity depends on energy transfer and kinetic momentum transfer, allowing determination of the potential function. Experiments reveal that the proton involved in intermolecular hydrogen bonding in N-methylacetamide and polyglycine I vibrates almost independently. An ionic representation (N(delta-)...H(+)...O(delta-)) of the hydrogen bond is more realistic than the normally accepted covalent model (NH...O). For polyglycine I, the proton experiences a local, symmetric double-minimum potential arising from dynamic exchange between the amide-like (CONH) and imidol-like (HOCN) forms of the peptide unit.

Microscopic motions in molten potassium spanning three frequency decades are studied by neutronscattering techniques. These comprise well-defined density oscillations and stochastic particle rearrangements and both are modeled on microscopic grounds. While vibratory motions are shown to share characteristics with those of their parent crystals, dynamic correlations between a diffusing particle and its neighbors can be accounted for only semiquantitatively.