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Séminaire exceptionnel MCBT

Vendredi 2 mars à 15h00,
Salle Louis Weil, E424.

Orateur : S. Autti, Lancaster University
"Breaking speed limits in the helium-3 universe"

Abstract

Contrary to common textbook knowledge, superfluid 3He-B seems to survive flows forced by an object moving at velocities far exceeding the critical Landau value (Nature Physics 12, 1017–1021 (2016)). That is, no mechanism for breaking bulk Cooper pairs exists even for arbitrarily fast uniform motion. In our current understanding, the Andreev-bound states on the surface (SABS) of the moving object are, however, emitted into the bulk, causing dissipation during acceleration at velocities above the Landau critical velocity. It is worth emphasizing that this dissipation is temperature independent at low temperatures and, hence, persists even in the zero-temperature limit --- in sharp contrast with the textbook picture of vanishing dissipation. Our experimental results imply that one can empty certain surface-bound Andreev bound states into the bulk in a controllable manner and then observe as they are replenished, providing insight into the dynamics of interaction between the gas of Bogoliubov excitations in the 3D topological superfluid and the corresponding gas of 2D edge states.

In this presentation I provide an overview of the above observations. I also discuss the role that surface specularity plays in the measurement, and show how we subtract the effect of single flux line (vortex) jumps in the moving superconducting instrument. I conclude by discussing our future plans of probing super-Landau superflows using in various superfluid phases including the polar phase where the Landau critical velocity is zero.

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