Topological order in solid state systems has been studied in condensed matter physics since the discovery of integer quantum Hall effect. But topological matter attracted considerable interest from the physics community after the proposals for possible observation of symmetry-protected topological phases (or the so-called topological insulators) in graphene, and experimental observation of a 2D topological insulator in CdTe/HgTe/CdTe quantum wells in 2007.