Ultrasonic Determination of the Superconducting Energy Gap in In2Bi

Abstract

The attenuation of longitudinal ultrasonic waves in the superconducting and normal states of the indium‐bismuth alloy of composition equivalent to the In₂Bi was measured at 60 Mc/sec by the double‐ended pulse‐echo technique. The decrease in attenuation below the superconducting critical temperature (5.6±0.1°K) and the temperature dependence of the superconducting energy gap were in reasonable agreement with the predictions of the BCS theory. The limiting energy gap at 0°K, 2 Δ (0), was determined as (3.4±0.2)kT_c. These results provide confirmation of Anderson's theory of dirty superconductors. The limiting critical field at 0°K was 870±10 G.