Enhancement of Casimir Friction between Graphene-Covered Topological Insulator

Casimir friction is theoretically studied between graphene-covered undoped bismuth selenide (Bi₂Se₃) in detail. In the graphene/Bi₂Se₃ composite structure, the coupling of the hyperbolic phonon polaritons supported by Bi₂Se₃ with the surface plasmons supported by graphene can lead to the hybrid surface plasmon-phonon polaritons (SPPPs). Compared with that between undoped Bi₂Se₃, Casimir friction can be enhanced by more than one order of magnitude due to the contribution of SPPPs. It is found that the chemical potential that can be used to modulate the optical characteristic of SPPPs plays an important role in Casimir friction. In addition, the Casimir friction between doped Bi₂Se₃ is also studied. The friction coefficient between doped Bi₂Se₃ can even be larger than that between graphene-covered undoped Bi₂Se₃ for suitable chemical potential due to the contribution of unusual electron surface states. The results obtained in this work are not only beneficial to the study of Casimir frictions but also extend the research ranges of topological insulators.