Observation of a new superfluid phase for ³He embedded in nematically ordered aerogel

Abstract

In bulk superfluid 3He at zero magnetic field, two phases emerge with the B phase stable everywhere except at high pressures and temperatures where the A phase is favored. Aerogels with nanostructure smaller than the superfluid coherence length are the only means to introduce disorder into the superfluid. Here we use a torsion pendulum to study 3He confined in an extremely anisotropic, nematically ordered aerogel consisting of roughly 10 nm thick alumina strands, spaced by about 100 nm, and aligned parallel to the pendulum axis. Kinks in the development of the superfluid fraction (at various pressures) as the temperature is varied correspond to phase transitions. Two such transitions are seen in the superfluid state, and we identify the superfluid phase closest to Tc at low pressure as the Polar state, a phase that is not seen in bulk 3He.