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Accueil du site > Évènements > Séminaires > Séminaires IRPHE > Archives IRPHE > 2023

Vendredi 13 janvier 2023 / IRPHE

publié le

Séminaire IRPHE

Direct visualization of the quantum vortex density law in rotating ⁴He

Orateur : Mathieu Gibert / Univ. Grenoble Alpes, Institut Néel

Abstract : When cooling the most common helium isotope at a temperature below 2.17 K along the vapor-liquid equilibrium, a very uncommon liquid phase called He II appears. One of its defining features is the existence of vortices whose core is as thin as a helium atom, as hypothesized by Feynman in the fifties. They are called quantum vortices and there is a quantization of the velocity circulation around them. They have been observed experimentally by indirect means, such as second sound attenuation or electron bubble imprints on photo sensitive material, and more recently but elusively by decorating them with hydrogen flakes. Here we show that we are able to visualize these vortices in the canonical case of a stationary rotating superfluid bucket. Using direct visualization, we quantitatively verify Feynman’s rule linking the resulting quantum vortex density to the imposed rotational speed. Our statistically meaningful results demonstrate that decorated quantum vortices behave as Feynman predicted. It follows that hydrogen flakes are good tracers for quantum vortices in a stationary case. With our methods, direct visualization of quantum vortex arrays is easily reproducible. Moreover, the vortex arrays aligned with the rotation axis that we observe (comparable with an Abrikosov lattice in superconductivity) can play the role of a well-defined and controlled initial condition for dynamical cases. Taking advantage of this setup, we present preliminary observations of collective wave mode propagation along quantum vortices and quantum vortex reconnections in rotating ⁴He.

Date et lieu : vendredi 13 janvier à 11h00, salle de séminaires IRPHE

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