Probing superfluid 4He with high-frequency nanomechanical resonators down to mK temperatures

Guénault, Tony and Guthrie, Andrew and Haley, Richard and Kafanov, Sergey and Pashkin, Yuri and Pickett, George and Poole, Malcolm and Schanen, Roch and Tsepelin, Viktor and Zmeev, Dmitry and Collin, Eddy and Maillet, Oliver and Gazizulin, Rasul (2019) Probing superfluid 4He with high-frequency nanomechanical resonators down to mK temperatures. Physical Review B: Condensed Matter and Materials Physics, 100: 020506. ISSN 2469-9969

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Abstract

Superfluids, such as superfluid 3He and 4He, exhibit a broad range of quantum phenomena and excitations which are unique to these systems. Nanoscale mechanical resonators are sensitive and versatile force detectors with the ability to operate over many orders of magnitude in damping. Using nanomechanical-doubly clamped beams of extremely high-quality factors Q>106, we probe superfluid 4He from the superfluid transition temperature down to mK temperatures at frequencies up to 11.6 MHz. Our studies show that nanobeam damping is dominated by hydrodynamic viscosity of the normal component of 4He above 1K. In the temperature range 0.3-0.8K, the ballistic quasiparticles (phonons and rotons) determine the beams' behavior. At lower temperatures, damping saturates and is determined either by magnetomotive losses or acoustic emission into helium. It is remarkable that all these distinct regimes can be extracted with just a single device, despite damping changing over six orders of magnitude.