Enhanced electron-phonon coupling in doubly aligned hexagonal boron nitride bilayer graphene heterostructure

Abstract

The relative twist angle in heterostructures of two-dimensional (2D) materials with similar lattice constants result in a dramatic alteration of the electronic properties. Here, we investigate the electrical and magnetotransport properties in bilayer graphene (BLG) encapsulated between two hexagonal boron nitride (hBN) crystals, where the top and bottom hBN are rotationally aligned with bilayer graphene with a twist angle $\theta_t\sim 0^{\circ} \text{and}~ \theta_b < 1^{\circ}$, respectively. This results in the formation of two moir\'e superlattices, with the appearance of satellite resistivity peaks at carrier densities $n_{s1}$ and $n_{s2}$, in both hole and electron doped regions, together with the resistivity peak at zero carrier density. Furthermore, we measure the temperature(T) dependence of the resistivity ($\rho$). The resistivity shows a linear increment with temperature within the range 10K to 50K for the density regime $n_{s1} <n<n_{s2}$ with a large slope d$\rho$/dT $\sim$ 8.5~$\Omega$/K. The large slope of d$\rho$/dT is attributed to the enhanced electron-phonon coupling arising due to the suppression of Fermi velocity in the reconstructed minibands, which was theoretically predicted, recently in doubly aligned graphene with top and bottom hBN. Our result establishes the uniqueness of doubly aligned moire system to tune the strength of electron-phonon coupling and to modify the electronic properties of multilayered heterostructures.