Two-dimensional (2D) atomic crystals, best exemplified by graphene, have
emerged as a new class of material that may impact future science and
technology. From a material physicist's point of view, 2D materials
provides vast opportunities on two fronts: first, the reduced
dimensionality in these 2D crystals often leads to novel material
properties that are different from those in the bulk; second, the entire
2D crystal is a surface, so it is possible to have better control of
their material properties with external perturbations. In this talk I
will illustrate these two points with examples. In particular, few-layer
MnBi2Te4 is an intrinsic magnetic topological insulator, and its
superior material quality has recently enabled us to observe the quantum
anomalous Hall effect; we are also able to exfoliate high temperature
superconductor Bi2Sr2CaCu2O8+d down to monolayer. We explore their
electronic properties while the doping and dimensionality of the 2D
systems are modulated.