| Popis: |
Ultrasonic attenuation in superconductors is used to study the temperature-dependent superconducting energy gap parameter Δ(T) in metal single crystals for different orientations of q with respect to the crystal axes. The electronic attenuation coefficients α s and α n for the superconducting and normal states at T are related to Δ(T) by the BCS equation $${{\alpha }_{s}}/{{\alpha }_{n}}=2{{\left[ \exp \left( \Delta \left( T \right)/kT \right)+1 \right]}^{-1}}$$ (1) The gap parameter at 0°K, Δ0, is obtained by extrapolation. Table I summarizes the most recent determinations of Δ0 for In. The ultrasonic values are significantly lower than the values determined by other methods. Anisotropy in Δ0 for the different orientations is probably not larger than the imprecision of the ultrasonic method (see also Table II). Since the In lattice, fct, departs so little from fcc, the superconducting energy gap would be expected to be nearly isotropic. |
