Thermodynamics of the A-B phase transition and the geometry of the A-phase gap nodes in superfluid He-3 at low temperatures

Since the A phase of superfluid He-3 has an energy gap with nodes while the B phase has a uniform gap, the entropies of the two phases are very different at low temperatures. The latent heat of the A-B transition is thus relatively large and provides a convenient probe for examining the structure of the A-phase gap nodes at low temperatures. We report here measurements of the latent heal down to similar to 150 mu K which show that at least to this temperature, the A-phase gap near the nodes is increasing linearly with deviation of the k vector from the nodal line. From the measurements of the latent heat and of the transition field B-AB we can determine the magnetization difference between the two phases.