Affiliation
National Institute for Materials Science
Title
Tunable energy gap and a phase transition in bilayer graphene/hexagonal boron nitride superlattices
Abstract
the quantum Hall regime of bilayer graphene (BLG) with a Landau level filling factor ν = 0, ‘magnetism’ is generally predicted whereby the system is spin- and/or valley/layer-polarized ground states.
Furthermore, the application of an electric field perpendicularly to BLG allows for tuning the energy gap at the charge neutrality point (CNP), leading to a promising candidate for future quantum devices. In a hexagonal boron nitride (hBN)/BLG moiré superlattice where crystallographic axes of BLG and hBN are aligned, an energy gap at the CNP is expected to open without an external electric field. Here we study the transport properties in hBN/BLG moiré superlattices with top and bottom gates (‘dual gate’) enabling individual modulation of the electric displacement field and carrier density. By measuring the temperature and dependence of the longitudinal resistivity at the CNP, we extract the energy gap Δ and demonstrate the tuning of Δ. Under a perpendicular magnetic field, transitions
between two insulating phases at the CNP are detected by varying the displacement field. It is found that there is no signature of a continuously vanishing Δ even in the vicinity of the criticality. This result agrees with a scenario of the formation of a microscopic network of the two competing phases at the first-order transition.