Abstract
Dirac cones in two dimensional systems such as those in graphene or on the surface of three dimensional topological insulators, have attracted a great attention recently. The robustness of Dirac points (Fermi surfaces) against weak perturbations are due to the nature of topological charges attached on these points. I will briefly review the background of quasiparticle interference, then I will apply the interference theory to visualizing topological charges of Dirac points, which can be detected by scanning tunneling microscopeexperiments. Basically, a Dirac-point that has topological charge N will leads to a 2N disconnected bright arc in its quasiparticle interference pattern.