It has become possible in recent years to fabricate and manipulate two-dimensional nanomaterials in the laboratory that are as thin as one to few atomic layers. A well-known example is graphene, where the Dirac-Weyl Hamiltonian for massless fermions describes the low-energy quasiparticles. Intriguing physics has been found in these few-layer systems, and phenomena originally associated with particle physics can now be observed in condensed matter systems. In this talk, I will focus on our recent theoretical and computational studies of a few representative systems. In particular, the quasiparticle states in rotated bilayer graphene systems act as massless fermions with two “flavors”, and interlayer coupling induces neutrino-like oscillations and anisotropic transport. In addition, a rare fractal-like “butterfly” energy spectrum arises under an external magnetic field. These two-dimensional atomic layer systems provide a unique platform to probe the rich physics involving multiple interacting massless fermions.