2020 Theses Doctoral

Gate Tunable Transport in Hexagonal Boron Nitride Encapsulated Bilayer Graphene

Tan, Cheng

Bilayer graphene has the linear band dispersion of monolayer graphene at high energies, but parabolic-like dispersion near charge neutrality. While the band structure is ordinarily without a gap, one can be introduced via an energy asymmetry between the layers. Experimentally, this can be done with dual electrostatic gating. By modifying the band structure, the electronic properties are expected to vary as well, though this variation is not well characterized. In this work I present on the electronic transport of bilayer graphene as the band gap and carrier densities are independently varied. By encapsulating the material in hexagonal boron nitride, the devices fabricated are clean and free from processing residue. In such a clean system, the electronic transport is determined by the properties of the material itself, and not extrinsic impurities. Near charge neutrality, this work indicates that the transport properties are driven by electron-hole scattering for the gapless case from approx 50K to 500K, and persists with the introduction of a band gap Delta. Away from charge neutrality, additional scattering mechanisms such as acoustic-phonon scattering and impurity scattering must be considered in addition with electron-hole scattering. The dominating scattering mechanism is dependent on temperature and chemical potential mu. This works showcases the properties of a hydrodynamic insulating state in bilayer graphene, where transport properties are determined by electron-hole scattering, even in the presence of a band gap.