The discovery of the Quantum Hall Effect (QHE) in graphene in 2005 constituted a major scientific breakthrough : it established the relativistic and chiral nature of charge carriers in this unique bi-dimensional material. Only one year later, the scientific community was again fascinated by the electronic properties of bilayer graphene… once again revealed by measuring the quantum Hall effect under intense magnetic field. Beside this exceptional discovery, it has been shown that two layers of graphene stacked upon each other do not behave as independent systems but, on the contrary, their mutual interaction gives rise to a “new” system with its “own” electronic properties.
Legend : a) quantization of the Hall resistance in graphene, bi-layer graphene and tri-layer graphene (experimental results obtained at LNCMI-T). b) Theoretical analysis and simulations establishing the rhombohedral stacking of trilayer graphene.
As a matter of fact, it was expected that the QHE in trilayer-graphene would be discovered very soon as theoretical studies were already being published… However, one had to wait until the end of 2011 for the first experimental studies to be reported. This long delay is partly due to the fact that the three layers of graphene constituting the system can actually be stacked upon each other in two different manners, thus making the interpretation of results more awkward. Furthermore, tri-layer graphene displays a much lower mobility than its graphene or bi-layer graphene counterparts so that the use of very intense magnetic field is required to achieve the QHEt. Within this line of research, our group was among the first to report on this long-lasting experimental evidence evidence . This pioneering experiment, spotted by Science News , will open the gate towards systematic and comprehensive experiments in order to understand the influence of the stacking order in the electronic properties of such systems… and hopefully establish the “missing link” between the properties of graphene and graphite.
D. P. Arovas & M. M. Fogler, University of California, San Diego, USA
F. Guinea, ICMM, Madrid, Spain
S. Roche, CI2N & ICREA, Barcelona, Spain
 Phys. Rev. Lett. 107, 126806 (2011)
 Science News, Web edition of 28th september 2011