Coulomb drag in graphene/hBN/graphene moir\'e heterostructures

TL;DR

This study observes Coulomb drag in graphene/hBN/graphene moiré heterostructures, revealing complex temperature and density-dependent behaviors that suggest non-Fermi liquid interactions between moiré mini-band carriers and original Dirac bands.

Contribution

First experimental observation of Coulomb drag in graphene/hBN moiré heterostructures, highlighting the interplay between mini-band and original Dirac band carriers.

Findings

Drag resistivity follows power laws at high T and n

Layer reciprocity breaks at low T, indicating energy drag

Moiré mini-band coupling deviates from simple Fermi liquid behavior

Abstract

We report on the observation of Coulomb drag between graphene-hexagonal boron nitride (hBN) moir\'{e} heterostructure with a moir\'{e} wavelength of $\sim$14 nm and an intrinsic graphene with a lattice constant of $\sim$0.25 nm. By tuning carrier densities of each graphene layer independently, we find that the charge carriers in moir\'{e} mini-bands, i.e., near the satellite Dirac point (sDP), can be coupled with the massless Fermions near the original Dirac point (oDP), strongly enough to generate a finite drag resistivity. At high temperature ($T$) and large density ($n$), the drag resistivities near both oDP and sDP follow a typical $n^{-\alpha}$ ($\alpha=1.3\sim1.7$) and $T^2$ power law dependence as expected for the momentum transfer process and it also satisfies the layer reciprocity. In contrast, at low $T$, the layer reciprocity is broken in both oDP-oDP and sDP-oDP coupled regions that suggest dominant energy drag. Furthermore, quantitatively, the drag resistivities near sDPs are smaller than those near oDP and they deviate from $T^2$ dependence below $\sim$100 K. These results suggest that the coupling between the carriers in moir\'{e} mini-bands and those in original Dirac bands may not be of a simple Fermi liquid nature.