The thermodynamics of the A-B transition in superfluid He-3 as a probe of the A-phase gap node geometry

We have used a magnetic held gradient to stabilise the phase boundary betwe en the A- and B-phases of superfluid He-3 inside a quasiparticle black body radiator down to 146 mu K; The radiator technique enables us to measure ve ry accurately the density of quasiparticle excitations and therefore the te mperature of the B-phase inside the radiator. As we ramp the held through t he transition we can observe the cooling (warming) effect when the volume o f A-phase is increased (decreased). From these measurements we deduce the t emperature dependence of the latent heat, which provides the lowest tempera ture verification yet of the existence of nodes in the A-phase order parame ter. (C) 2000 Elsevier Science B.V. All rights reserved.