Mapping the twist angle and unconventional Landau levels in magic angle graphene

Understand

The emergence of flat electronic bands and of the recently discovered strongly correlated and superconducting phases in twisted bilayer graphene crucially depends on the interlayer twist angle upon approaching the magic angle $\theta_M \approx 1.1\deg$.

• Although advanced fabrication methods allow alignment of graphene layers with global twist angle control of about 0.1$\deg$, little information is currently available on the distribution of the local twist angles in actual magic angle twisted bilayer graphene (MATBG) transport devices.
• Here we map the local $\theta$ variations in hBN encapsulated devices with relative precision better than 0.002$\deg$ and spatial resolution of a few moir$\'e$ periods.
• Utilizing a scanning nanoSQUID-on-tip, we attain tomographic imaging of the Landau levels in the quantum Hall state in MATBG, which provides a highly sensitive probe of the charge disorder and of the local band structure determined by the local $\theta$.