AbstractEvidence of fluctuations in transport have long been predicted in 3He. They are expected to contribute only within 100μK of Tc and play a vital role in the theoretical modeling of ordering; they encode details about the Fermi liquid parameters, pairing symmetry, and scattering phase shifts. It is expected that they will be of crucial importance for transport probes of the topologically nontrivial features of superfluid 3He under strong confinement.

Because of the extreme purity, lack of disorder, and complex order parameter, the first-order superfluid 3He A–B transition is the leading model system for first order transitions in the early universe. Here we report on the path dependence of the supercooling of the A phase over a wide range of pressures below 29.3 bar at nearly zero magnetic field. The A phase can be cooled significantly below the thermodynamic A–B transition temperature.

We provide the conversion parameters to allow a 3He melting curve thermometer to be used to calibrate secondary thermometers to the PLTS2000 temperature scale (Rusby et al. in J Low Temp Phys 149(3):156, 2007). Additional fits to the phase diagram of superfluid 3He are also provided using the melting curve P, T measurements and of the phase diagram of superfluid 3He (Greywall in Phys Rev B 33(11):7520, https://doi.org/10.1103/PhysRevB.33.7520, 1986) as a bridge.

Precise measurements of the dissipation and resonant frequency of a torsion pendulum reveal an anomaly in the inferred viscosity and normal density of liquid 3He near the superfluid transition. We present an argument that the anomaly originates in the large viscosity and large viscosity change of the normal component in the torsion tube in the vicinity of the superfluid transition. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.

We examine the discontinuous first-order superfluid He3 A to B transition in the vicinity of the polycritical point (2.232 mK and 21.22 bar). We find path-dependent transitions: cooling at fixed pressure yields a well-defined transition line in the temperature-pressure plane, but this line can be reliably crossed by depressurizing at nearly constant temperature after transiting Tc at a higher pressure. This path dependence is not consistent with any of the standard B-phase nucleation mechanisms in the literature.

Superfluid 3He, with unconventional spin-triplet p-wave pairing, provides a model system for topological superconductors, which have attracted significant interest through potential applications in topologically protected quantum computing. In topological insulators and quantum Hall systems, the surface/edge states, arising from bulk-surface correspondence and the momentum space topology of the band structure, are robust.

The investigation of transport properties in normal liquid helium-3 and its topological superfluid phases provides insights into related phenomena in electron fluids, topological materials, and putative topological superconductors. It relies on the measurement of mass, heat, and spin currents, due to system neutrality. Of particular interest is transport in strongly confining channels of height approaching the superfluid coherence length, to enhance the relative contribution of surface excitations, and suppress hydrodynamic counterflow.

In superfluid He3-B confined in a slab geometry, domain walls between regions of different order parameter orientation are predicted to be energetically stable. Formation of the spatially modulated superfluid stripe phase has been proposed. We confined He3 in a 1.1 μm high microfluidic cavity and cooled it into the B phase at low pressure, where the stripe phase is predicted. We measured the surface-induced order parameter distortion with NMR, sensitive to the formation of domains. The results rule out the stripe phase, but are consistent with 2D modulated superfluid order.

Liquid helium-3 and helium-4 are remarkable substances. They are quantum liquids, meaning that their behavior is governed by the laws of quantum mechanics. Because of their small atomic mass, each isotope exists in a liquid state down to the temperature of absolute zero. And at sufficiently low temperature, each becomes a superfluid. However, the two isotopes have very different properties because 3He is a fermion and 4He is a boson. As a result of their different statistics, superfluidity in 3He appears at a temperature one-thousandth of that at which superfluid 4He forms.