Electric Field-Induced Hole- and Electron-Type Flat Bands in Twisted Double Bilayer Graphene

Abstract

Application of a finite electric field and small twist angle between two graphene bilayers leads to widely tunable electronic structures that support emergent phenomena. Here, we measure the electronic structure of twisted double bilayer graphene with twist angles of 3.1${}^{\circ }$ and 6.0${}^{\circ }$ using micro-focused angle-resolved photoemission spectroscopy (microARPES) on \textit{in situ} gated samples. At a twist angle of 6.0${}^{\circ }$, we find that the dispersion around the valence and conduction band extrema is unchanged compared to separate graphene bilayers, whereas electric field tunable hybridisation gaps and band flattening effects occur at higher binding energies. In the 3.1${}^{\circ }$ structure, we find that the resulting superlattice drives dispersion changes around the valence and conduction band edges. Increasing the gate-induced doping in the bottom bilayer leads to the formation of flat bands between the valence band maximum in the bottom bilayer and conduction band minimum in the top bilayer. Our experiments establish combinations of twist angle and electric field that potentially support strong electron-hole excitations and that provide a benchmark for the theoretical description of moderately twisted double bilayer graphene.

arXiv comment19 pages, 5 figures

References in corpus (27)

• The electronic properties of graphene
• Magic-angle graphene superlattices: a new platform for unconventional superconductivity
• Correlated Insulator Behaviour at Half-Filling in Magic Angle Graphene Superlattices
• Graphene Bilayers with a Twist
• Spin-polarized Correlated Insulator and Superconductor in Twisted Double Bilayer Graphene
• Evidence of high-temperature exciton condensation in 2D atomic double layers
• Moiré heterostructures as a condensed matter quantum simulator
• Tunable Moiré Bands and Strong Correlations in Small-Twist-Angle Bilayer Graphene
• Correlated states in twisted double bilayer graphene
• Evidence for an excitonic insulator phase in 1T-TiSe${}_2$
• Nearly Flat Chern Bands in Moiré Superlattices
• Correlated Insulating States in Twisted Double Bilayer Graphene
• Electrically tunable correlated and topological states in twisted monolayer-bilayer graphene
• Tunable correlation-driven symmetry breaking in twisted double bilayer graphene
• Theory of correlated insulating behaviour and spin-triplet superconductivity in twisted double bilayer graphene
• Flatbands in twisted double bilayer graphene
• Band structure and topological property of twisted double bilayer graphenes
• Van Hove Singularities and Excitonic Effects in the Optical Conductivity of Twisted Bilayer Graphene
• Correlated electron-hole State in Twisted Double Bilayer Graphene
• Superconductivity in Twisted Double Bilayer Graphene Stabilized by WSe${}_2$
• Gap Opening in Twisted Double Bilayer Graphene by Crystal fields
• Band-unfolding approach to Moirè-induced band-gap opening and Fermi-level-velocity reduction in twisted bilayer graphene
• Observation of Electrically Tunable van Hove Singularities in Twisted Bilayer Graphene from nanoARPES
• New Mechanism for Strongly Bound Excitons in Gapless Two-Dimensional Structures
• Combined minivalley and layer control in twisted double bilayer graphene
• Scattering between minivalleys in a moiré material
• ARPES signatures of few-layer twistronic graphenes