Nanoscale detection of valley-dependent spin splitting around atomic defects of graphene

Knowing exact nature of broken-symmetry states around individual atomic defects of graphene is very important in understanding the electronic properties. Here, we realize measurement of valley-dependent spin splitting around atomic defects of graphene at nanoscale and single-electron level by using edge-free graphene quantum dots. Our experiments detect large valley-dependent spin splitting around atomic defects of graphene due to the coexistence of sublattice symmetry breaking, enhanced spin-orbit coupling and time reversal symmetry breaking. The spin splitting in the two distinct valleys has opposite direction and almost has the same amplitude. The strategy reported in this work is quite robust and could be extended to measure broken-symmetry states in other 2D systems.