Broadening of the surface Andreev bound states band of superfluid He-3-B on a partially specular wall

A measurement of the surface Andreev bound states of the superfluid He-3-B phase under different boundary conditions is presented. Transverse-acoustic impedance spectroscopy was used to determine the bandwidth of the bound states on a wall with various specularities. It was found that the band was broader for larger specularity and filled up the superfluid gap above a critical specularity. Specularity was controlled by coating the wall with thin layers of He-4 and was evaluated separately using acoustic impedance measurement in the normal-fluid phase.