Tunable graphene phononic crystal

Abstract

In the field of phononics, periodic patterning controls vibrations and thereby the flow of heat and sound in matter. Bandgaps arising in such phononic crystals realize low-dissipation vibrational modes and enable applications towards mechanical qubits, efficient waveguides, and state-of-the-art sensing. Here, we combine phononics and two-dimensional materials and explore the possibility of manipulating phononic crystals via applied mechanical pressure. To this end, we fabricate the thinnest possible phononic crystal from monolayer graphene and simulate its vibrational properties. We find a bandgap in the MHz regime, within which we localize a defect mode with a small effective mass of 0.72 ag = 0.002 mphysical. Finally, we take advantage of graphene’s flexibility and mechanically tune a finite size phononic crystal. Under electrostatic pressure up to 30 kPa, we observe an upshift in frequency of the entire phononic system by more than 350%. At the same time, the defect mode stays within the bandgap and remains localized, suggesting a high-quality, dynamically tunable mechanical system.

Mechanical metal-insulator transition in 2D graphene phononic crystals

“…23,31,32 For out-of-plane modes (solid lines) we find a bandgap between 48.8 and 56.4 MHz (blue shaded), in agreement with previous work. 23,30 The entire phononic lattice behaves like a thin membrane with vibrational mode frequencies f determined by the built-in tension ( ~√ ). Also, in agreement with previous work, we find that an increase in uniform tension (σxx/σyy = 1) leads to monotonic upscaling of both the top of valence (fVB) and bottom of conduction band (fCB) frequencies as shown in Fig.…”

“…[22][23][24][25] The resulting tunable (biaxial) tension allows broad tunability of the of the bandgap centre frequency. 23 Nevertheless, the topology of the bands in the systems explored so far has not been affected by tension -i.e. a gapped system remained gapped at any tension level.…”

“…[19][20][21] In contrast, it has been recently demonstrated that the tension in much more flexible two-dimensional (2D) materials can be dynamically controlled by applying electrostatic pressure via an external gate electrode. [22][23][24][25] The resulting tunable (biaxial) tension allows broad tunability of the of the bandgap centre frequency. 23 Nevertheless, the topology of the bands in the systems explored so far has not been affected by tension -i.e.…”

Graphene-Based Nanoelectromechanical Periodic Array with Tunable Frequency

“…Although the resonant frequencies of eigenmodes are discrete for a single unit cell, hybridization among unit cells gives rise to the formation of phonon bands. 35−38 First, we model the device using a model with infinitely repeated unit cells, 37,47 which we refer as "infinite model", to calculate the band structure. The few-layer graphene flake is modeled as an infinite isotropic thin plate and is considered to be fully clamped on the periodic nanopillar array.…”

“…Recently, achieving PnCs using graphene and other 2D materials has been proposed 35−37 and experimentally verified. 37,38 However, these studies mainly focus on optical approaches, and electrical tunability of 2D materials-based PnCs, to our knowledge, has never been experimentally demonstrated.…”