The Unique Superfluid 3He A-B Interface: Surface Tension and Contact Angle

We have measured the A-B boundary wall contact angle and the phase interface surface tension in superfluid 3 He. The measurements have been made in the ballistic temperature regime at zero pressure in magnetic fields up to 400 mT. We infer the surface energies from the behaviour of the phase boundary moving in and out of a stack of glass capillary tubes. We measure the wall contact angle from the observed capillary height and obtain the interphase surface tension from the level of over- or under-magnetisation when the interface "pops" out of the capillaries. This is the first measurement of both the surface tension and contact angle in high magnetic fields.