Landau quantization in graphene monolayer, Bernal bilayer, and Bernal trilayer on graphite surface

Abstract

Electronic properties of surface areas decoupled from graphite are studied using scanning tunnelling microscopy and spectroscopy. We show that it is possible to identify decoupled graphene monolayer, Bernal bilayer, and Bernal trilayer on graphite surface according to their tunnelling spectra in high magnetic field. The decoupled monolayer and bilayer exhibit Landau quantization of massless and massive Dirac fermions, respectively. The substrate generates a sizable band gap, ~35 meV, in the Bernal bilayer, therefore, the eightfold degenerate Landau level at the charge neutrality point is split into two valley-polarized quartets polarized on each layer. In the decoupled Bernal trilayer, we find that both massless and massive Dirac fermions coexist and its low-energy band structure can be described quite well by taking into account only the nearest-neighbor intra-and interlayer hopping parameters. A strong correlation between the Fermi velocity of the massless Dirac fermions and the effective mass of the massive Dirac fermions is observed in the trilayer. Our result demonstrates that the surface of graphite provides a natural ideal platform to probe the electronic spectra of graphene layers.

Observation of chirality transition of quasiparticles at stacking solitons in trilayer graphene

“…Figure 3(d) shows high-field spectra of the ABA TLG, which exhibit a sequence of LLs peaks of both massless Dirac fermions (l = 1) and massive Dirac fermions (l = 2). The energies of the LLs for the l = 1 and l = 2 fermions are described by [9,14,26] ..., 2 , …”

Experimental evidence for non-Abelian gauge potentials in twisted graphene bilayers

“…The surface 2 few-layer of HOPG usually decouples from the bulk 15,21,[24][25][26][27] and, more importantly, the twisted graphene bilayers with various rotation angles, especially the small rotation angles, can be easily observed on HOPG surface 21 . Therefore, the surface of HOPG provides a natural ideal platform to verify the fundamental prediction: the existence of non-Abelian gauge potentials in twisted graphene bilayers 4 .…”

Landau quantization of Dirac fermions in graphene and its multilayers

“…Interestingly, Bernal trilayer (ABA) graphene exhibits the coexistence of massless and massive Dirac fermions. The various types of quasiparticles give rise to disparate Landau quantized behaviors in graphene monolayers, Bernal bilayers, and Bernal trilayers, which have been frequently observed on different substrates, especially on graphite surfaces [45,58,70,71]. Graphite -a three-dimensional (3D) allotrope of carbon -consists of stacks of graphene layers with Bernal layer-stacking that are weakly coupled by van der Waals forces [43].…”

“…Graphite -a three-dimensional (3D) allotrope of carbon -consists of stacks of graphene layers with Bernal layer-stacking that are weakly coupled by van der Waals forces [43]. The surface monolayer/few-layer graphene may electronically decouple from graphite when the separation between the topmost graphene layers and the graphite is larger than the equilibrium distance of ∼0.34 nm [45,57,72] or when the sheets have a large rotation angle with respect to the substrate after exfoliation [73]. Hence, it is possible to detect the Landau quantization of 2D Dirac fermions for graphene monolayers and multilayers on the surfaces of such 3D systems [74].…”

“…The 2D nature of the quasiparticles even exists in four-layer graphene [44]. More importantly, the quasiparticles in graphene multilayers exhibit a strong layer number [45] and stacking-order dependency [46], leading to the distinct Landau quantized behaviors and rich quantum Hall physics [47][48][49][50][51]. This makes it possible to identify the number of layers and the stacking configurations of graphene by using the LL spectrum.…”