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

TL;DR

This paper investigates the subtle symmetry-breaking effects in graphene on hBN, revealing ultra-low energy gaps and spin-orbit interactions that suggest topologically non-trivial states, using resistively-detected electron spin resonance.

Contribution

It provides the first measurement of sublattice splitting and intrinsic spin-orbit coupling in graphene/hBN heterostructures at ultra-low energies.

Findings

Sublattice splitting of ~20 μeV measured

Intrinsic spin-orbit coupling of ~45 μeV confirmed

Results suggest a topologically non-trivial state in the material

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, owing to the low energy scale of the terms involved (few tens of ueV). These low energy terms include sublattice splitting, the Rashba 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 measure a sublattice splitting of the order of 20E-6 eV, and confirm an intrinsic spin orbit coupling of approximately 45E-6 eV. The dominance of the latter suggests a topologically non-trivial state, involving fascinating properties. Electron spin resonance is a promising route towards unveiling the intriguing band structure at low energy scales.