Transport of bound quasiparticle states in a two-dimensional boundary superfluid

Autti, Samuli and Haley, Richard and Jennings, Ash and Pickett, George and Poole, Malcolm and Soldatov, Arkady and Tsepelin, Viktor and Vonka, Jakub and Zavyalov, Vladislav and Zmeev, Dmitry (2023) Transport of bound quasiparticle states in a two-dimensional boundary superfluid. Nature Communications, 14: 6819. ISSN 2041-1723

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Abstract

The B phase of superfluid 3He can be cooled into the pure superfluid regime, where the thermal quasiparticle density is negligible. The bulk superfluid is surrounded by a quantum well at the boundaries of the container, confining a sea of quasiparticles with energies below that of those in the bulk. We can create a non-equilibrium distribution of these states within the quantum well and observe the dynamics of their motion indirectly. Here we show that the induced quasiparticle currents flow diffusively in the two-dimensional system. Combining this with a direct measurement of energy conservation, we conclude that the bulk superfluid 3He is effectively surrounded by an independent two-dimensional superfluid, which is isolated from the bulk superfluid but which readily interacts with mechanical probes. Our work shows that this two-dimensional quantum condensate and the dynamics of the surface bound states are experimentally accessible, opening the possibility of engineering two-dimensional quantum condensates of arbitrary topology.