The superfluid glass phase of ³ He-A

It is established theoretically that an ordered state with continuous symmetry is inherently unstable to arbitrarily small amounts of disorder. This principle is of central importance in a wide variety of condensed systems including superconducting vortices, Ising spin models and their dynamics, and liquid crystals in porous media, where some degree of disorder is ubiquitous, although its experimental observation has been elusive. On the basis of these ideas, it was predicted that ³ He in high-porosity aerogel would become a superfluid glass. We report here our nuclear magnetic resonance measurements on ³ He in aerogel demonstrating destruction of long-range orientational order of the intrinsic superfluid orbital angular momentum, confirming the existence of a superfluid glass. In contrast, ³ He-A generated by warming from superfluid ³ He-B has perfect long-range orientational order providing a mechanism for switching offthis effect.