Anomalous attenuation of longitudinal ultrasound in intermediate state   of high pure type I superconductor
  The dependence of the ultrasonic attenuation on the direction of magnetic field in an intermediate state of the very pure Gallium single crystal, in the case, when the magnetic field H is perpendicular to the wave vector k at the temperature T = 0.5 K, is found to be anomalously different from the dependence, observed at the same temperature and the magnitude of magnetic field equal to the critical magnetic field H=Hc in a normal state of superconductor. This new phenomenon can be explained, considering the anisotropy of the Fermi surface in the very pure Gallium single crystal. 
Anatoly G. Shepelev, Oleg P. Ledenyov and Genady D. Filimonov
cond-mat.supr-con cond-mat.mtrl-sci physics.ins-det