Z. Fisk

Lattice dynamics of the A 15 compound Nb 3 Sb

The phonon dispersion curves of Nb/sub 3/Sb have been studied by inelastic neutron scattering. All the branches have been determined in the main symmetry directions and the results are analyzed with Born--von Karman models of different complexity. A model with general forces up to the eighth-nearest neighbors gives excellent agreement with experiment. However, a rather good description of the dispersion curves is obtained with a model including axially symmetric forces up to the third-nearest neighbors, which indicates that these interactions are dominant. Temperature effects were found to be very small. Additional experiments were performed on polycrystalline samples to determine directly the phonon density of states. Our results obtained on Nb/sub 3/Sb are compared with the available phonon data on Nb/sub 3/Sn.

Lattice dynamics of the A15 compound Nb/sub 3/Sb

The phonon dispersion curves of Nb/sub 3/Sb have been studied by inelastic neutron scattering. All the branches have been determined in the main symmetry directions and the results are analyzed with Born--von Karman models of different complexity. A model with general forces up to the eighth-nearest neighbors gives excellent agreement with experiment. However, a rather good description of the dispersion curves is obtained with a model including axially symmetric forces up to the third-nearest neighbors, which indicates that these interactions are dominant. Temperature effects were found to be very small. Additional experiments were performed on polycrystalline samples to determine directly the phonon density of states. Our results obtained on Nb/sub 3/Sb are compared with the available phonon data on Nb/sub 3/Sn.

FERMI SURFACE MEASUREMENTS IN A-15 COMPOUNDS

Publisher Summary It is believed that electronic and/or phononic structure is responsible for the unusual normal state of high-Tc superconductivity. The de Haas–van Alphen (dHvA) effect provides the most direct and highest precision method of Fermi surface determination presently known. This chapter presents new dHvA data in Nb3Sb and compares that data with the various band calculations, while at the same time reviewing the progress of Fermi surface measurements in A15 compounds in general. In the chapter, three separate pieces of Fermi surface are observed that are consistent with cylindrical surfaces and centered at the M point in the Brillouin zone. Excellent topological correspondence and rough quantitative agreement between theory and experiment for the higher frequencies is also explained. The chapter presents not only a qualitative agreement but also a great deal of quantitative agreement that exists between experiment and band structure calculation. The wave function character at Ep is primarily d-like and coming from Nb sites, a rigid band shift can be useful if one recognizes that results are only qualitative.