Title: Ultralow Dissipation Nanomechanical Devices from Monocrystalline Silicon Carbide

Abstract: Due to their low mass and long coherence times, nanomechanical resonators have many applications, from biomolecule mass sensing to hybrid quantum interfaces. In many instances the performance is limited by internal material damping. Crystalline materials promise lower material dissipation, however due to fabrication challenges, amorphous materials are more commonly utilized. Crystalline silicon carbide (SiC) is particularly appealing due to its exquisite mechanical, electrical and optical properties, but to-date exhibits higher nanomechanical dissipation than both amorphous and other crystalline materials. To address this, we fabricate nanomechanical resonators thinned from bulk monocrystalline 4H-SiC. Characterization of multiple resonators of different sizes and thicknesses, allows us to discern the surface and volumetric contributions to dissipation. We measure mechanical dissipation rates as low as 2.7 mHz, more than an order-of-magnitude lower than any previous crystalline SiC resonator, yielding quality factors as high as 20 million at room temperature. We also quantify the nonlinear dissipation of SiC nanomechanical resonators for the first time, finding that it is lower than other materials. This promises higher sensitivity in applications such as mass sensing. By achieving exceptionally low dissipation in SiC resonators, our work provides a path towards improved performance in sensing and other applications.