Stability of Superfluid 3He-B in Compressed Aerogel

In recent work, it was shown that new anisotropic p-wave states of superfluid He-3 can be stabilized within high-porosity silica aerogel under uniform positive strain. In contrast, the equilibrium phase in an unstrained aerogel is the isotropic superfluid B phase. Here we report that this phase stability depends on the sign of the strain. For a negative strain of similar to 20% achieved by compression, the B phase can be made more stable than the anisotropic A phase, resulting in a tricritical point for A, B, and normal phases with a critical field of similar to 100 mT. From pulsed NMR measurements, we identify these phases and the orientation of the angular momentum.