Inhomogeneous quantum groups are shown to be an effective algebraic tool in the study of integrable systems. The method is illustrated on the one-dimensional Heisenberg ferromagnet whose symmetry is investigated by means of the quantum Galilei group GAMMA(q)(1) here introduced. Both the single magnon and the s = 1/2 bound states of n magnons are completely described by the algebra. Therefore, some of the results provided by the Bethe-ansatz method emerge as a natural consequence of the quantum symmetry of the discrete chain.

High-temperature series expansions of the spin-spin correlation functions of the RP(n-1) spin model on the square lattice are computed through order beta8 for general spin dimensionality n. Tables are reported for the expansion coefficients of the energy per site, the susceptibility, and the second correlation moment.

It is found that the magnitude of the weak-localization (WL) correction to the conductance in a lateral superlattice (LSL) differs considerably from that in a homogeneous two-dimensional electron gas. The LSL effects were observed by measuring the dependence of the magnetoconductance on the strength of a modulated potential in silicon inversion layers. For parallel transport in a LSL the WL is enhanced, while it is reduced for perpendicular transport. This agrees with a recent theory for WL in a LSL. The effect is larger for stronger potential modulation and its maximum value deduced from the experiments is 2.8.

The structures of the two reconstructed phases of the Pt(100) surface have been studied by high-resolution helium diffraction. In contrast to earlier investigations, we show that for both phases the superstructure in the approximate [011] direction is not fivefold but much larger. The mean distance between atom rows in the top layer, however, is very close to that of a fivefold superstructure. This supports the description of the surface layer in a model which assumes static oscillations about a flat and equidistant atom arrangement. The results are discussed in comparison with low-energy electron diffraction, scanning-tunneling-microscopy, and x-ray-diffraction results.

Several experiments were carried out to study the origin of the anomalous photovoltaic effect in high-quality YBa2Cu3O7 thin films. In particular, the issue of whether the signal is induced by thermal gradients was addressed. Using samples with well-characterized orientation and texture, and using low-power cw lasers, it was determined that the signal was proportional to the thermal gradient along the c axis. However the magnitude of the signal was more than 10 times larger than that produced by thermoelectric power. Additionally, the temperature dependence of this photovoltaic signal was found to be very sample dependent even for high-quality films where all the resistance-temperature curves were apparently the same. The photovoltaic signal may be related to the recently discovered time-dependent photoinduced changes in superconductivity.

Positive-muon (mu+) spin-relaxation experiments have been carried out in a pressed-powder sample of the low-carrier-density heavy-electron system YbBiPt. Spatially inhomogeneous and disordered static Yb magnetism is observed below approximately 0.5 K, with a strongly reduced Yb moment of approximately 0.1-mu(B) over approximately 50% of the sample volume at T=0.06 K. Substantial mu+ spin-lattice relaxation, rarely observed in heavy-electron systems, suggests anomalously slow Yb spin fluctuations. Our data are reminiscent of mu+ behavior in spin glasses, and raise the question of whether the large low-temperature specific heat in YbBiPt is due in part to low-lying magnetic excitations.