The interlayer electronic coupling in twisted bilayer graphene results in band anticrossing of the intersected Dirac cones. The shifts of the two new band extrema relative to the original intersection point are crucial for the electronic and optical properties. However, such shifts, particularly, the possible asymmetric band repulsion in the band anticrossing, are still elusive. Here, using infrared spectroscopy, we reveal the asymmetric band repulsion for twisted bilayer graphene under ambient pressure and with pressure up to 4 GPa. The optical resonance peak undergoes redshift under pressure, in stark contrast to natural bilayer and multilayer graphene. In conjunction with tight-binding calculation, we also reveal that twisted bilayer graphene exhibits a notably smaller out-of-plane elastic constant than that of the natural bilayer. Our study paves the way for mechanical tuning of the transport and optoelectronic properties of twisted bilayer graphene, in particular, achieving flat bands in broader twist angles.

Close

PrevNext

View figure in article

• High-pressure studies
• Van Hove singularity
• 2-dimensional systems
• Twisted bilayer graphene
• Infrared spectroscopy