Chiral symmetry breaking induced gap and flat band in a correlated graphene

The low-energy excitations of graphene are relativistic massless Dirac fermions with opposite chiralities at K and K' valleys. Breaking the chiral symmetry could lead to gap opening (in analogy to mass generation in quantum electrodynamics) and other intriguing phenomena. Despite many theoretical predictions, so far experimental realization of chiral symmetry breaking (CSB) in a real honeycomb lattice has been missing. Here I will present our recent experimental work on graphene with large CSB induced gap. In addition, a flat band is observed near the Fermi energy, opening up new opportunity for investigating correlated physics and interaction driven superconductivity.