Coulomb drag and electrical polarization in graphene-hBN moiré systems

DongKeun Ki

Department of Physics and HK Institute of Quantum Science & Technology, The University of Hong Kong, Pokfulam Road, Hong Kong, China

When two (nearly) identical 2D crystals are stacked together, a quasi-periodic moiré structure on a scale much larger than either of the two constituents can be formed that generates new electronic band structures. Moreover, by tuning the moiré length scale, one can approach strong coupling regime where Coulomb interactions between the carriers are strongly enhanced, leading to many-body states. Here, we discuss some of our on-going works to investigate layer-dependent transport and polarizations in 2D moiré systems. First, we will show that charge carriers in moiré mini-bands formed in graphene aligned with hBN can be strongly coupled with those in original Dirac bands by measuring Coulomb drag in graphene-hBN-graphene moiré heterostructures (arXiv:2405.20393). This study demonstrates that Coulomb drag experiment can be used to investigate interlayer interactions in 2D moiré systems. Second, we will report on an unexpected finding of large electric polarization and ratchet effect in graphene on double bilayer hBN interface. We will present all necessary experimental details and some possible origins. Lastly, we will discuss potential impacts of our works and possible new directions. Financial supports from the MOST China (2020YFA0309600) and the UGC/RGC of Hong Kong SAR (AoE/P-701/20, C7037-22G, 17300020, 17300521, and 17309722) are acknowledged.