Spectroscopic study of the surface density of states of superfluid 3He by transverse acoustic impedance measurements

The surface density of states (SDOS) in superfluid (3)He at a diffusive wall was investigated by systematic measurements of the transverse acoustic impedance Z. The observed difference between the temperature dependence of Z in the A and B phases can be explained by a difference in the SDOS of each phase. In the B phase, an additional gap in the SDOS opened between the upper energy edge Delta(*) of the surface Andreev bound states band and the bulk energy gap Delta. The temperature dependence of Delta(*) was measured and was about 30% smaller than the theoretical value. In the A phase, a flat and gapless SDOS was confirmed experimentally.