The Interacting Energy Bands of Magic Angle Twisted Bilayer Graphene Revealed by the Quantum Twisting Microscope

TL;DR

This study uses the quantum twisting microscope to directly image and analyze the energy bands of magic angle twisted bilayer graphene, revealing interaction-driven band transformations and electron duality that explain its complex quantum phases.

Contribution

The paper demonstrates the use of the quantum twisting microscope to directly observe the interacting energy bands of MATBG with high resolution, uncovering the dual nature of electrons and interaction effects.

Findings

Interaction-induced bandwidth renormalization observed.

Mott-like cascades of heavy particles identified.

Dirac revivals of light particles detected.

Abstract

Electron interactions in quantum materials fundamentally shape their energy bands and, with them, the material's most intriguing quantum phases. Magic angle twisted bilayer graphene (MATBG) has emerged as a model system, where flat bands give rise to a variety of such phases, yet the precise nature of these bands has remained elusive due to the lack of high-resolution momentum space probes. Here, we use the quantum twisting microscope (QTM) to directly image the interacting energy bands of MATBG with unprecedented momentum and energy resolution. Away from the magic angle, the observed bands closely follow the single-particle theory. At the magic angle, however, we observe bands that are completely transformed by interactions, exhibiting light and heavy electronic character at different parts of momentum space. Upon doping, the interplay between these light and heavy components gives rise to a variety of striking phenomena, including interaction-induced bandwidth renormalization, Mott-like cascades of the heavy particles, and Dirac revivals of the light particles. We also uncover a persistent low-energy excitation tied to the heavy sector, suggesting a new unaccounted degree of freedom. These results resolve the long-standing puzzle in MATBG - the dual nature of its electrons - by showing that it originates from electrons at different momenta within the same topological heavy fermion-like flat bands. More broadly, our results establish the QTM as a powerful tool for high-resolution spectroscopic studies of quantum materials previously inaccessible to conventional techniques.