The change in bending rigidity with temperature $\kappa (T)$ for 2D materials is highly debated: theoretical works predict both increase and decrease. Here we present measurements of $\kappa (T)$, for a 2D material: $AB$-stacked bilayer graphene. We obtain $\kappa (T)$ from phonon dispersion curves measured with helium atom scattering in the temperature range 320–400 K. We find that the bending rigidity increases with temperature. Assuming a linear dependence over the measured temperature region we obtain $\kappa (T)=[(1.3\pm 0.1)+(0.006\pm 0.001)T/K]\mathrm{eV}$ by fitting the data. We discuss this result in the context of existing predictions and room temperature measurements.

• Received 20 May 2021
• Accepted 28 October 2021

DOI:https://doi.org/10.1103/PhysRevLett.127.266102