MÖSSBAUER STUDY OF LATTICE SOFTENING AND PHONON MOMENTS IN SUPERCONDUCTING COMPOUNDS

C. Kimball , F. Fradin

The temperature dependence of the Mössbauer shift and recoil-free fraction for the β-W pseudobinary compounds V3GaxSn1-x, (x = 0.9, 0.5, 0.1) has been measured in an experiment designed to contrast the lattice properties of high and low Tc superconductors. For V3Ga0.9Sn0.1 (Tc ~ 11 K) a deviation of the thermal shift δ(T) from Debye behavior is shown to be due to lattice softening. Using a quasiharmonic model the temperature dependence of the Debye temperature is obtained. At low temperature the ratio of shift/Debye-Waller factor is proportional to the ratio of phonon-moments < ω > / < ω-1 > which represent the phonon-only part of the electron-phonon coupling parameter in McMillan's theoretical treatment of strong-coupled superconductors. A Mössbauer measure of < ω > / < ω-1 > in the temperature region from 4 to 50 K in the V3GaxSn1-x system indicates a weaker dependence on concentration than expected from the electron-phonon coupling parameter derived from Tc. A model of the phonon-spectral density which consists of two Debye spectra is used to obtain the temperature-dependent frequency shifts for the anharmonic (high Tc) compound. The electronic contribution to the temperature-dependent shift is calculated on the basis of a model density-of-states, which accounts for the temperature and concentration dependence of the susceptibility, electronic specific heat and nuclear spin-lattice relaxation rate. The lattice shift with increasing temperature is of opposite sign to that of the isomer shift.

Domaines: Articles anciens

C. Kimball, F. Fradin. MÖSSBAUER STUDY OF LATTICE SOFTENING AND PHONON MOMENTS IN SUPERCONDUCTING COMPOUNDS. Journal de Physique Colloques, 1974, 35 (C6), pp.C6-383-C6-383. ⟨10.1051/jphyscol:1974671⟩. ⟨jpa-00215828⟩