It has been shown that the relative stabilities of various superfluid states of 3He can be influenced by anisotropy in a silica aerogel framework. We prepared a suite of aerogel samples compressed up to 30% for which we performed pulsed NMR on 3He im
bibed within the aerogel. We identified A and B-phases and determined their magnetic field-temperature phase diagrams as a function of strain. From these results we infer that the B-phase is distorted by negative strain forming an anisotropic superfluid state more stable than the A-phase.
In recent work it was shown that new anisotropic p-wave states of superfluid 3He can be stabilized within high porosity silica aerogel under uniform positive strain [1]. In contrast, the equilibrium phase in an unstrained aerogel, is the isotropic su
perfluid B-phase [2]. Here we report that this phase stability depends on the sign of the strain. For negative strain of ~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 ~100 mT. From pulsed NMR measurements we identify these phases and the orientation of the angular momentum.
It is established theoretically that an ordered state with continuous symmetry is inherently unstable to arbitrarily small amounts of disorder [1, 2]. This principle is of central importance in a wide variety of condensed systems including supercondu
cting vortices [3, 4], Ising spin models [5] and their dynamics [6], and liquid crystals in porous media [7, 8], where some degree of disorder is ubiquitous, although its experimental observation has been elusive. Based on these ideas it was predicted [9] that 3He in high porosity aerogel would become a superfluid glass. We report here our nuclear magnetic resonance measurements on 3He 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, 3He-A generated by warming from superfluid 3He-B has perfect long-range orientational order providing a mechanism for switching off this effect.
