Tunable graphene phononic crystal

TL;DR

This paper demonstrates a tunable graphene-based phononic crystal where mechanical pressure adjusts vibrational bandgaps and localized defect modes, enabling dynamic control of phononic properties in ultra-thin materials.

Contribution

It introduces a mechanically tunable phononic crystal made from monolayer graphene, combining phononics with 2D materials and demonstrating dynamic frequency control.

Findings

A bandgap in the MHz regime was observed in the graphene phononic crystal.

Mechanical pressure up to 30 kPa causes a frequency upshift of over 350%.

The defect mode remains localized within the bandgap during tuning.

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 $m_{physical}$. 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.