The experimental observation of quantum Hall effect of lD3 chiral quasiparticles in trilayer graphene

The linear dispersion of the low-energy electronic structure of monolayer graphene supports chiral quasiparticles that obey the relativistic Dirac equation and have a Berry phase of € (refs,). In bilayer graphene, the shape of the energy bands is quadratic, and its quasiparticles have a chiral degree, l=2, and a Berry phase of 2 €. These characteristics are usually determined from quantum Hall effect (QHE) measurements in which the Berry phase causes shifts in Shubnikov-de Haas (SdH) resistance oscillations. The QHE in graphene also exhibits an unconventional sequence of plateaux of Hall conductivity, xy, with quantized steps of 4e 2 /h, except for the first plateau, where it is governed by the Berry phase. Here, we report magnetotransport measurements in ABC-stacked trilayer graphene, and their variation with carrier density, magnetic field and temperature. Our results provide the first evidence of the presence of l=3 chiral quasiparticles with cubic dispersion, predicted to occur in ABC-stacked trilayer graphene. The SdH oscillations we observe suggest Landau levels with four-fold degeneracy, a Berry phase of 3 €, and the marked increase of cyclotron mass near charge neutrality. We also observe the predicted unconventional sequence of QHE plateaux, xy =±6e 2 /h, ±10e 2 /h, and so on.