Ultrasonic attenuation in niobium I: Purity dependence in normal and Meissner states, measurements and theory

摘要: The attenuation of 30-70 MHz longitudinal sound waves has been measured in both the normal and superconducting Meissner states from 1.2 K to 10 for several crystals niobium with resistance ratios 83-3880. This corresponds measurements ql<1 (q is wavevector l electron mean free path). In state an approximately T-3 term observed path, which can be caused by interband scattering. On entering this contribution modified leads deviations simple BCS behaviour. However, it shown that are too large explained alone theoretical arguments developed explain terms a mechanism will lead apparently purity dependent energy gap near Tc.