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

The influence of confinement on the topological phases of superfluid 3He is studied using the torsional pendulum method. We focus on the phase transition between the chiral A-phase and the time-reversal-invariant B-phase, motivated by the prediction of a spatiallymodulated (stripe) phase at the A-B phase boundary. We confine superfluid 3He to a single 1.08 {\mu}m 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. This has a non-monotonic pressure dependence, suggesting that a new intrinsic B-phase nucleation mechanism operates under confinement, mediated by the putative stripe phase. 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.Comment: 6 figures, 1 table + supplemental informatio

Intertwined superfluid and density wave order in two-dimensional 4He

Superfluidity is a manifestation of the operation of the laws of quantum mechanics on a macroscopic scale. The conditions under which superfluidity becomes manifest have been extensively explored experimentally in both quantum liquids (liquid 4He being the canonical example) and ultracold atomic gases1, 2, including as a function of dimensionality3, 4. Of particular interest is the hitherto unresolved question of whether a solid can be superfluid5, 6. Here we report the identification of a new state of quantum matter with intertwined superfluid and density wave order in a system of two-dimensional bosons subject to a triangular lattice potential. Using a torsional oscillator we have measured the superfluid response of the second atomic layer of 4He adsorbed on the surface of graphite, over a wide temperature range down to 2 mK. Superfluidity is observed over a narrow range of film densities, emerging suddenly and subsequently collapsing towards a quantum critical point. The unusual temperature dependence of the superfluid density in the limit of zero temperature and the absence of a clear superfluid onset temperature are explained, self-consistently, by an ansatz for the excitation spectrum, reflecting density wave order, and a quasi-condensate wavefunction breaking both gauge and translational symmetry

Early infant HIV-1 diagnosis programs in resource-limited settings: opportunities for improved outcomes and more cost-effective interventions

Early infant diagnosis (EID) of HIV-1 infection confers substantial benefits to HIV-infected and HIV-uninfected infants, to their families, and to programs providing prevention of mother-to-child transmission (PMTCT) services, but has been challenging to implement in resource-limited settings. In order to correctly inform parents/caregivers of infant infection status and link HIV-infected infants to care and treatment, a 'cascade' of events must successfully occur. A frequently cited barrier to expansion of EID programs is the cost of the required laboratory assays. However, substantial implementation barriers, as well as personnel and infrastructure requirements, exist at each step in the cascade. In this update, we review challenges to uptake at each step in the EID cascade, highlighting that even with the highest reported levels of uptake, nearly half of HIV-infected infants may not complete the cascade successfully. We next synthesize the available literature about the costs and cost effectiveness of EID programs; identify areas for future research; and place these findings within the context of the benefits and challenges to EID implementation in resource-limited settings

Size modulated transition in the fluid-structure interaction losses in nano mechanical beam resonators

An understanding of the dominant dissipative mechanisms is crucial for the design of a high-Q doubly clamped nanobeam resonator to be operated in air. We focus on quantifying analytically the viscous losses-the squeeze film damping and drag force damping-that limit the net quality factor of a beam resonator, vibrating in its flexural fundamental mode with the surrounding fluid as air at atmospheric pressure. Specifically, drag force damping dominates at smaller beam widths and squeeze film losses dominate at larger beam widths, with no significant contribution from structural losses and acoustic radiation losses. The combined viscous losses agree well with the experimentally measured Q of the resonator over a large range of beam widths, within the limits of thin beam theory. We propose an empirical relation between the maximum quality factor and the ratio of maximum beam width to the squeeze film air gap thickness. Published by AIP Publishing