UC Riverside

Graphene is a two-dimensional honeycomb lattice of carbon atoms. Since it is experimentally isolated in 2004, this 2D system becomes the prevailing platform for condensed matter physics. The band structures of single, bilayer and trilayer graphene differ dramatically. And it can be strongly dependent on stacking order in trilayer grahene. In this dissertation, we present comprehensive transport studies on double-gated trilayer graphene, exciting platform for study of such interplay, where the relative strengths of single particle physics and interaction effects are tunable via external parameters such as gate voltage and magnetic field. I will start with a brief introduction of graphene electron configuration including the density of state, Fermi energy and quantum Hall effect. Next I will discuss the energy band structure of single, bi-, trilayer graphene with the tight binding calculation. In chapter 3, I will describe how dual-gated suspended graphene devices are fabriacted. One of the strong advantages for the suspended structures is to remove the extrinsic factor with post current-annealing technique which can achieve the high quality samples on dual-gated ABA and ABC trilayer graphene. These studies are discussed in chapters five through seven. First, we focus on the observation of quantum Hall effect in ABA trilayer graphene. We demonstrate the symmetry broken states at the lowest Landau level. By applying out-of-plane electric field E⊥, we observe degeneracy breaking and transitions between QH plateaus. Secondly, we study a intrinsic gap of ABC trilayer graphene at the charge neutrality point with zero electric and magnetic fields. This gap can be partially suppressed by an electric field of either polarity and parallel magnetic field. By tuning temperature we found this gapped insulating state has a critical temperature suggesting a phase transition underlying symmetries of this correlated electron phenomena.

Lastly, we discuss broken symmetry quantum Hall states in dual-gated ABC trilayer graphene devices. We observe that the sequence of quantum Hall plateaus depends strongly on the interlayer potential bias and an intriguing "hexagon" pattern, which can be accounted for by a model based on crossings between symmetry-broken LLs reflecting the interplay between single particle remote hopping and interaction-induced symmetry breaking.