Negative vacuum friction in terahertz gain systems
Lixin Ge
Abstract
Two objects in relative motion without physical contact suffer a friction force, resulting from vacuum fluctuation. It is widely accepted that friction acts in the opposite direction of the relative velocity. Here, this study demonstrates the existence of negative friction, where the direction of friction is along the sliding direction, in a gain system. The system consists of a vacuum-separated silica sphere and a dielectric substrate covered by a graphene sheet (gain medium). The friction torque of the rotating sphere can be switched between positive and negative, depending on the quasi-Fermi energy of graphene. Negative vacuum friction can be achieved when the quasi-Fermi energy is large, and its magnitude is strongly dependent on the distance, temperature, and permittivity of the substrate. For moderate conditions, the torque generated by negative friction surpasses the resistance posed by the surrounding air, presenting a different approach for driving nanoparticles to an ultrahigh rotating speed.Received 17 May 2023Accepted 31 May 2023DOI:https://doi.org/10.1103/PhysRevB.108.045406©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCasimir effectFrictionSurface plasmon polaritonPhysical SystemsGrapheneCondensed Matter, Materials & Applied Physics