ABSTRACT
Finding new phenomena in condensed matter is strongly linked to the discovery, synthesis, or fabrication of new materials and, even more importantly, to the quality of them. Semiconductor heterojunctions, that is, layered structures composed of two or more semiconductors, are a good example of this. ™e discovery of the integer (Klitzing et al. 1980) and fractional quantum Hall e£ects (QHEs) (Tsui et al. 1982) was possible due to the expertise developed in the growth of interfaces between properly doped GaAs and AlGaAs semiconductors. ™e two-dimensional (2D) electron gas conšned at the interface of these two semiconductors was hiding surprising physics, unveiled only when the growth techniques were mastered and the mobility of the 2D electrons was suÀciently high. Nowadays, a novel material, graphene, is responsible for the renewed interest in 2D electronic systems. ™e term graphene refers to a one-atom thick layer of carbon atoms arranged in a 2D honeycomb lattice. It can be considered as the starting material for other low-dimensional carbon-based systems. For instance, it can be wrapped to form fullerenes, rolled into one-dimensional (1D) nanotubes, or stacked to form graphite. ™eoretically, graphene has been studied for almost 60 years, but it was only recently that it was fully appreciated that graphene also provides an excellent playground for “condensed-matter quantum electrodynamics.” ™is has
spurred the interest of this material beyond the limits of the condensed-matter physics community.
