The strange case of Al10V: well defined local modes in a metallic solid

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Abstract
Detailed measurements have been made of the anomalous low-temperature heat capacity and electrical resistivity of the intermetallic compound Al10V. Both properties (and also the thermal expansion) are dominated by Einstein-like behaviour with a sharply defined characteristic temperature of 23+or-1K, and an excitation of the same energy has been seen with inelastic neutron scattering. An upper limit on the level width is 2K, so that hybridisation with band phonons appears to be unimportant. The compound is atomically well ordered, and there is one Al site whose environment is unusual and of the right kind to give a low-lying vibrational mode. A sample doped with Ga showed a second level, of energy about 10K, associated with preferential occupation of the special site by Ga. The structure that gives rise to this local mode in Al10V appears to be accidental, a consequence of strong directional bonding between Al and V elsewhere in the unit cell. No other example is known of such a well defined local mode in a metallic solid.