# Large-area, periodic, and tunable intrinsic pseudo-magnetic fields in low-angle twisted bilayer graphene

## TL;DR

This study provides the first experimental evidence of large-area, tunable pseudo-magnetic fields in low-angle twisted bilayer graphene, revealing vortex lattices and pseudo-Landau levels, and demonstrates control via rotation and strain.

## Contribution

It experimentally confirms the existence of tunable pseudo-magnetic fields in twisted bilayer graphene and shows how to manipulate their properties through geometric and strain modifications.

## Key findings

- Observation of vortex lattices matching moiré patterns
- Detection of pseudo-Landau levels via STM/STS
- Pseudo-magnetic fields can be tuned by rotation angle and heterostrain

## Abstract

A properly strained graphene monolayer or bilayer is expected to harbour periodic pseudo-magnetic fields with high symmetry, yet to date, a convincing demonstration of such pseudo-magnetic fields has been lacking, especially for bilayer graphene. Here, we report the first definitive experimental proof for the existence of large-area, periodic pseudo-magnetic fields, as manifested by vortex lattices in commensurability with the moir\'e patterns of low-angle twisted bilayer graphene. The pseudo-magnetic fields are strong enough to confine the massive Dirac electrons into circularly localized pseudo-Landau levels, as observed by scanning tunneling microscopy/spectroscopy, and also corroborated by tight-binding calculations. We further demonstrate that the geometry, amplitude, and periodicity of the pseudo-magnetic field can be fine-tuned by both the rotation angle and heterostrain applied to the system. Collectively, the present study substantially enriches twisted bilayer graphene as a powerful enabling platform for exploration of new and exotic physical phenomena, including quantum valley Hall effects and quantum anomalous Hall effects.