Quantum-Dot Assisted Spectroscopy of Degeneracy-Lifted Landau Levels in Graphene

TL;DR

This paper demonstrates the use of atomic-sized quantum dots bound to defects in hexagonal Boron Nitride as sensitive probes for energy spectroscopy of Landau levels in graphene, revealing symmetry-breaking gaps and high Landé g-factors.

Contribution

It introduces a novel quantum dot-based spectroscopy method that minimizes screening and enhances sensitivity to interacting states in graphene under high magnetic fields.

Findings

Detection of degeneracy lifting with magnetic field at ground and excited states

Observation of symmetry-broken gaps developing steeply with magnetic field

Measurement of high Landé g-factors up to 160

Abstract

Energy spectroscopy of strongly interacting phases requires probes which minimize screening while retaining spectral resolution and local sensitivity. Here we demonstrate that such probes can be realized using atomic sized quantum dots bound to defects in hexagonal Boron Nitride tunnel barriers, placed at nanometric distance from graphene. With dot energies capacitively tuned by a planar graphite electrode, dot-assisted tunneling becomes highly sensitive to the graphene excitation spectrum. The spectra track the onset of degeneracy lifting with magnetic field at the ground state, and at unoccupied exited states, revealing symmetry-broken gaps which develop steeply with magnetic field - corresponding to Land\'e $g$ factors as high as 160. Measured up to $B = 33$ T, spectra exhibit a primary energy split between spin-polarized excited states, and a secondary spin-dependent valley-split. Our results show that defect dots probe the spectra while minimizing local screening, and are thus exceptionally sensitive to interacting states.