W. J. L. Buyers

Ferroelectric ordering in the relaxor Pb(Mg1/3Nb2/3)O-3 as evidenced by low-temperature phonon anomalies

Neutron scattering measurements of the lowest-energy TO phonons in the relaxor Pb(Mg 1 / 3 Nb 2 / 3 )O 3 (PMN) are reported for 10≤T7≤50 K. The soft mode, which is overdamped by the polar nanoregions below the Burns temperature T d =620 K, surprisingly recovers below 220 K. The square of the soft-mode energy (∞ω 0 ) 2 increases linearly with decreasing temperature and is consistent with the behavior of a ferroelectric soft mode. At 10 K, ∞ω 0 reaches II meV, the same value observed in ferroelectric Pb(Zn 1 / 3 Nb 2 / 3 )O 3 at low T. An unusual broadening of the TA phonon starts at T d and disappears at 220 K, coincident with the recovery of the TO mode. These dynamics suggest that a well-developed ferroelectric state is established below 220 K.

From incommensurate to dispersive spin-fluctuations : The high-energy inelastic spectrum in superconducting YBa2Cu3O6.5

We have investigated the spin-fluctuations at energy transfers up to

Dynamic stripes and resonance in the superconducting and normal phases of YBa2Cu3O6.5 ortho-II superconductor

\ensuremath{\sim}110\phantom{\rule{0.3em}{0ex}}\mathrm{meV}

Neutron scattering search for static magnetism in oxygen-ordered YBa2Cu3O6.5

, well above the resonance energy

Effect of the pseudogap on suppressing high energy inelastic neutron scattering in superconducting YBa2Cu3O6.5

(33\phantom{\rule{0.3em}{0ex}}\mathrm{meV})

Spin dynamics near the critical doping in weakly superconducting underdoped YBa2Cu3O6.35 (Tc=18K)

in the

Temperature evolution of the quantum gap in CsNiCl3

\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.5}

Strict Limit on In-Plane Ordered Magnetic Dipole Moment in URu2Si2

ortho-II superconductor using neutron time-of-flight and triple-axis techniques. The spectrum at high energies differs from the low-energy incommensurate modulations previously reported where the incommensurate wave vector is largely independent of energy. Well above the resonance the peak of the spin response lies at wave vectors that increase with energy. Within error the excitations at all energies above the resonance are best described by a ring around the

Neutron scattering investigation of the d - d excitations below the Mott gap of CoO

(\ensuremath{\pi},\ensuremath{\pi})

Evidence for decay of spin waves above the pseudogap of underdoped YBa2Cu3O6.35

position. The isotropic wave-vector pattern differs from a recently reported square pattern in different but related systems. The spin spectral weight at high energies is similar to that in the insulator but the characteristic velocity is