Deviation from the normal mode expansion in a coupled graphene-nanomechanical system

Cornelia Schwarz (1) , Benjamin Pigeau (2) , Laure Mercier de Lépinay (2) , Aurélien G. Kuhn (2) , Dipankar Kalita (1) , Nedjma Bendiab (1) , Laëtitia Marty (1) , Vincent Bouchiat (1) , Olivier Arcizet (2)

1 NEEL - Quan2m - Interactions modulables dans des états quantiques 2D
2 NEEL - NOF - Nano-Optique et Forces

We optomechanically measure the vibrations of a nanomechanical system made of a graphene membrane suspended on a silicon nitride nanoresonator. When probing the thermal noise of the coupled nanomechanical device, we observe a significant deviation from the normal mode expansion. It originates from the heterogeneous character of mechanical dissipation over the spatial extension of coupled eigenmodes, which violates one of the fundamental prerequisite for employing this commonly used description of the nanoresonators' thermal noise. We subsequently measure the local mechanical susceptibility and demonstrate that the fluctuation-dissipation theorem still holds and permits a proper evaluation of the thermal noise of the nanomechanical system. Since it naturally becomes delicate to ensure a good spatial homogeneity at the nanoscale, this approach is fundamental to correctly describe the thermal noise of nanomechanical systems which ultimately impact their sensing capacity.

Domaines: Physique Quantique [quant-ph]; Electrons fortement corrélés [cond-mat.str-el]

Cornelia Schwarz, Benjamin Pigeau, Laure Mercier de Lépinay, Aurélien G. Kuhn, Dipankar Kalita, et al.. Deviation from the normal mode expansion in a coupled graphene-nanomechanical system. Physical Review Applied, 2016, 6 (6), pp.064021. ⟨10.1103/PhysRevApplied.6.064021⟩. ⟨hal-01237910⟩