Anisotropy of Superfluid 3He Near Free Surface Investigated by Surface State Electrons

摘要

We have measured the resistivity of a Wigner solid formed on the free surface of superfluid 3He in the A and B phases under magnetic fields. The mobility of the Wigner solid is limited by the collisions of thermally excited quasiparticles in 3He, and hence is very sensitive to the distribution of quasiparticles in momentum space. The observed resistivity of the Wigner solid in the A phase asymptotically approaches the temperature-square dependence at low temperatures, reflecting the A phase gap with point nodes. Its temperature dependence is well explained by the [^(l)]hat{boldsymbol{l}} vector being uniformly aligned normal to the surface. The resistivity in the B phase, in contrast, exhibits an exponential decrease at low temperatures. The resistivity in the small field well agrees with the behavior expected for the isotropic gap in the BW state. The resistivity increases in high magnetic fields, which is explained by the combination of the distortion of the gap in the BW state by the field and the orientation of the order parameter caused by the free surface.