The A-B transition in superfluid helium-3 under confinement in a thin slab geometry

Abstract

The influence of confinement on the phases of superfluid helium-3 is studied using the torsional pendulum method. We focus on the transition between the A and B phases, where the A phase is stabilized by confinement and a spatially modulated stripe phase is predicted at the A–B phase boundary. Here we discuss results from superfluid helium-3 contained in a single 1.08-μm-thick nanofluidic cavity incorporated into a high-precision torsion pendulum, and map the phase diagram between 0.1 and 5.6 bar. We observe only small supercooling of the A phase, in comparison to bulk or when confined in aerogel, with evidence for a non-monotonic pressure dependence. This suggests that an intrinsic B-phase nucleation mechanism operates under confinement. Both the phase diagram and the relative superfluid fraction of the A and B phases, show that strong coupling is present at all pressures, with implications for the stability of the stripe phase.

A Polka-Dot Pattern Emerges in Superfluid Helium

“…2(a). The A-B transition was observed at T AB ¼ 0.7T bulk c in agreement with torsional oscillator measurements, with a 1.08 μm cavity [33]. As we previously observed in the 0.7 μm cavity, the B phase nucleated stochastically in two spin-orbit orientations with distinct NMR signatures: stable B þ and metastable B − [32,39].…”

“…To optimize the formation of stripes in this work we chose a slab geometry of height D ¼ 1.1 μm, where the B phase is stable down to zero pressure [33]. The stripe phase was originally predicted in the weak-coupling limit of Bardeen-Cooper-Schrieffer theory [27], while the strongcoupling corrections to this theory in general favor the A phase and suppress the stability of stripes [30].…”

“…The stripe phase was originally predicted in the weak-coupling limit of Bardeen-Cooper-Schrieffer theory [27], while the strongcoupling corrections to this theory in general favor the A phase and suppress the stability of stripes [30]. At present the strong coupling effects are not fully understood theoretically, leaving the stability of the stripe phase an open question [30,33]. We performed the experiment at low pressure to minimize the strong-coupling effects.…”

Half-quantum vortices and walls bounded by strings in the polar-distorted phases of topological superfluid 3He

“…In nanostructured confinement, i.e. in thin slabs 36,71 or in various aerogels, 14,[72][73][74][75] the phase diagram, as well as the symmetry group of the normal phase, can be altered in a controlled fashion. In the presence of commercially available nematically ordered material called nafen, 14 the three-dimensional continuous rotational symmetry SO(3) L in Eq.…”

Atomically Layered Helium Films at Ultralow Temperatures: Model Systems for Realizing Quantum Materials

“…This strategy is particularly suitable for the study of topological superfluid 3 He in the quasi-2D limit, k −1 F ≪ D < 10 0 . So far cavities of height D in the range 1000-100 nm have been studied [124][125][126][127][128]. An advantage is that for fixed cavity height the effective confinement 0 ∕D is tuneable by pressure, since…”