By driving with a microwave pulse the lowest frequency antiferromagnetic resonance of the quasi-1D biaxial antiferromagnet ͑C 2 H 5 NH 3 ͒ 2 CuCl 4 into an unstable region, intrinsic localized spin waves have been generated and detected in the spin wave gap. These findings are consistent with the prediction that nonlinearity plus lattice discreteness can lead to localized excitations with dimensions comparable to the lattice constant.

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It is found that in some metals an intrinsic localized mode may exist with frequency above the top of the phonon spectrum. The necessary condition, requiring sufficiently high ratio of quartic to cubic anharmonicity may be fulfilled because of screening of the interaction between ions by free electrons. Starting from the known literature values of the pair potentials we have found that in Ni and Nb the derived localized mode condition is fulfilled. MD simulations of the nonlinear dynamics of Ni and Nb confirmed that high frequency ILMs may exist in these metals.

Optically-induced real-time impurity modes are used to shepherd intrinsic localized vibrational modes (discrete breathers) along micromechanical arrays via either attractive or replulsive interactions. Adding an electrode to the cantilever array provides control of the sign of lattice anharmonicity, hence allowing both hard and soft nonlinearities to be studied. A number of dynamical effects are demonstrated and explained, including the optical tweezing of localized vibrational energy in a nonlinear lattice. PACS

A comprehensive characterization of the compound Fe 2 VAl was carried out. Samples grown by arc melting or the Bridgman method have Al and Fe deficiencies of up to 5 at. %. Czochralski-grown samples were Fe rich and Al deficient. X-ray diffraction implies appreciable antisite disorder in all of our samples. Fourier-transform infrared (FTIR) spectroscopy measurements showed that the carrier density and scattering time had little sample-to-sample variation or temperature dependence for near-stoichiometric samples. FTIR and dc resistivity suggest that the transport properties of Fe 2 VAl are influenced by both localized and delocalized carriers, with the former primarily responsible for the negative temperature coefficient of resistivity. Magnetization measurements reveal that near-stoichiometric samples have superparamagnetic clusters with at least two sizes of moments. We conclude that in Fe 2 VAl, antisite disorder causes significant modification to the semimetallic band structure proposed theoretically. With antisite disorder considered, we are now able to explain most of the physical properties of Fe 2 VAl. None of our data suggest heavy-fermion behavior in our samples. A comprehensive characterization of the compound Fe 2 VAl was carried out. Samples grown by arc melting or the Bridgman method have Al and Fe deficiencies of up to 5 at. %. Czochralski-grown samples were Fe rich and Al deficient. X-ray diffraction implies appreciable antisite disorder in all of our samples. Fourier-transform infrared ͑FTIR͒ spectroscopy measurements showed that the carrier density and scattering time had little sample-to-sample variation or temperature dependence for near-stoichiometric samples. FTIR and dc resistivity suggest that the transport properties of Fe 2 VAl are influenced by both localized and delocalized carriers, with the former primarily responsible for the negative temperature coefficient of resistivity. Magnetization measurements reveal that near-stoichiometric samples have superparamagnetic clusters with at least two sizes of moments. We conclude that in Fe 2 VAl, antisite disorder causes significant modification to the semimetallic band structure proposed theoretically. With antisite disorder considered, we are now able to explain most of the physical properties of Fe 2 VAl. None of our data suggest heavy-fermion behavior in our samples. Keywords Physics and Astronomy