Nonlinear Response of Nanoelectromechanical Resonators in Trapped Superfluid Vortex States

Morrison, Nathaniel and Kafanov, Sergey (2021) Nonlinear Response of Nanoelectromechanical Resonators in Trapped Superfluid Vortex States. Masters thesis, Lancaster University.

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Abstract

Nanoelectromechanical resonators are useful as both probes and generators of turbulence in superfluid helium. Individual quantum vortices may become “trapped” by a doubly-clamped beam-type resonator, permitting probing of a single vortex line in isolation. This opens the door for studies of the fundamental processes governing the transfer and dissipation of energy in quantum turbulence at the smallest of length scales. As the small-scale limit of the Kelvin cascade is as yet poorly investigated, this is of great interest in the drive to understand how energy is ultimately returned to the environment in turbulent superfluid. In this thesis, evidence of single-vortex dynamics directly influencing resonator response is presented, via analysis of the transmission of a doubly-clamped beam resonator in the presence of quantum vortices. A length of vortex extending from the resonator beam to the substrate results in greatly increased dissipation, damping, and turbulence nucleation. The vortex also introduces a large, negative nonlinear restoring force. These effects are attributed to the motion of the vortex filament. These results demonstrate the ability of the nanoelectromechanical scheme to transduce motion on single vortex lines and recommends the system for future studies investigating the evolution of Kelvin waves.