Detecting degeneracy and subtle broken-symmetry states of graphene at nanoscale

TL;DR

This paper reports the first direct measurement of degeneracy and broken-symmetry states in graphene at the nanoscale, revealing defect-induced exotic electronic states through high-resolution quantum dot techniques.

Contribution

It introduces a novel method using edge-free graphene quantum dots to measure valley and spin splittings at the single-electron level, uncovering defect-related phenomena.

Findings

Large valley splitting near atomic defects

Enhanced spin-orbit coupling around defects

Detection of exotic electronic states in graphene

Abstract

Measuring degeneracy and broken-symmetry states of a system at nanoscale requires extremely high energy and spatial resolution, which has so far eluded direct observation. Here, we realize measurement of the degeneracy and subtle broken-symmetry states of graphene at nanoscale for the first time. By using edge-free graphene quantum dots, we are able to measure valley splitting and valley-contrasting spin splitting of graphene at the single-electron level. Our experiments detect large valley splitting around atomic defects of graphene due to the coexistence of sublattice symmetry breaking and time reversal symmetry breaking. Large valley-contrasting spin splitting induced by enhanced spin-orbit coupling around the defects is also observed. These results reveal unexplored exotic electronic states in graphene at nanoscale induced by the atomic defects.