The atoms in these ultimately thin crystals are all placed at the surface. It makes them accessible to study and control directly with external stimulus such as gate or tunneling electrodes, light, local magnetic fields etc. Their experimental research over the past decade made fundamental contributions to the understanding of matter-excitation in all crystalline systems.
Moreover, the collective crystal excitation sometimes dress up as new particles (which are ether very hard to realize or fundamentally not allowed in the empty free space) and teach us physics over extremely wide spectrum. For example, how ultra relativistic Fermions in graphene can ignore high energy barriers.
In our research, therefore, we also try to realize conceptually new systems, or to push the well known systems into new configurations. In particular, where we expect interesting correlations and interactions between the particles. The fact that it is very hard to predict what type of orders and phenomena will emerge in these cases, makes the experimental observations both fascinating and crucial.