Neutron scattering measurements of the lowest-energy TO phonons in the relaxor Pb(Mg 1/3 Nb 2/3 )O3 (PMN) are reported for 10 ≤ T ≤ 750 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 (hω0) 2 increases linearly with decreasing temperature, and is consistent with the behavior of a ferroelectric soft mode. At 10 K hω0 reaches 11 meV, the same value observed in ferroelectric Pb(Zn 1/3 Nb 2/3 )O3 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.

A continuum of magnetic states has been observed by neutron scattering from the spin-1 chain compound CsNiCl3 in its disordered gapped one-dimensional phase. Results using both triple-axis and time-of-flight spectrometers show that around the antiferromagnetic point Qc = pi, the continuum lies higher in energy than the Haldane gapped excitations. At 6 K the integrated intensity of the continuum is about 12(2)% of the total spectral weight. This result is considerably larger than the 1%-3% weight predicted by the nonlinear sigma model for the three-particle continuum.

The magnetic spectrum at high energies in heavily underdoped YBa 2 Cu 3 O 6.35 ͑T c =18 K͒ has been determined throughout the Brillouin zone. At low energy, the scattering forms a cone of spin excitations emanating from the antiferromagnetic ͑0.5,0.5͒ wave vector with an acoustic velocity similar to that of insulating cuprates. At high-energy transfers, below the maximum energy of 270 meV at ͑0.5,0͒, we observe zone-boundary dispersion much larger and spectral weight loss more extensive than in insulating antiferromagnets. Moreover, we report phenomena not found in insulators, an overall lowering of the zone-boundary energies and a large damping of ϳ100 meV of the spin excitations at high energies. The energy above which the damping occurs coincides approximately with the gap determined from transport measurements. We propose that as the energy is raised, the spin excitations encounter an extra channel of decay into particle-hole pairs of a continuum that we associate with the pseudogap.