Sublattice symmetry breaking and ultralow energy excitations in graphene-on-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>h</mml:mi><mml:mi>BN</mml:mi></mml:math> heterostructures

Abstract

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 $\ensuremath{\mu}\mathrm{eV}$). 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 $\ensuremath{\mu}\mathrm{eV}$, and we confirm an intrinsic spin orbit coupling of approximately 45 $\ensuremath{\mu}\mathrm{eV}$. 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.