Sublattice symmetry breaking and ultra low energy excitations in Graphene-on-hBN Heterostructures

The low-lying states of graphene contain exciting topological properties that depend on the interplay of different symmetry-breaking terms. The corresponding energy gaps remained unexplored until recently due to the low-energy scale of the terms involved (few tens of μeV). These low-energy terms include sublattice splitting, the Rashba coupling, and the intrinsic spin-orbit coupling, whose balance determines the topological properties. In this work, we unravel the contributions arising from the sublattice and the intrinsic spin orbit splitting in graphene on hexagonal boron-nitride. Employing resistively detected electron spin resonance, we identify a sublattice splitting of the order of 20 μeV, and we confirm an intrinsic spin orbit coupling of approximately 45 μeV. The dominance of the latter suggests a topologically nontrivial state, involving fascinating properties. Electron spin resonance is a promising route toward unveiling the intriguing band structure at low-energy scales.