Transport studies of dual-gated ABA- and ABC-stacked trilayer graphene

We present electrical transport studies of dual-gated ABA- and ABC-stacked trilayer graphene field effect transistors. Employing high-quality thin HfO$_{2}$ layers as the top and back gate dielectrics, we independently tune the carrier density and control the band structure of trilayer graphene via the application of a perpendicular electric field E$_{perp}$. The large gating efficiency of the two gates (5.53 x 10$^{12} $/cm$^{2}$ per Volt) and their high breakdown voltage ($>$ 6 V) enable us to reach exceedingly large carrier densities and E$_{perp}$ values, which results in wide tuning of the conductivity of the trilayer devices. Results on ABA-stacked trilayer graphene confirm its semi-metallic nature and reveal evidence of the band structure changes induced by E$_{perp}$. The resistance at the charge neutrality point of ABC-stacked trilayer graphene increases by many orders of magnitude with increasing E$_{perp}$ due to the gradual opening of a band gap. Our results suggest a saturation of the gap size at perpendicular displacement fields greater than 3.5 V/nm, in agreement with theoretical calculations.