Exploring Quantum Geometry with Terahertz Light: A Breakthrough in Twisted Bilayer Graphene

A recent groundbreaking study led by ICFO researchers, in collaboration with several international research groups, has uncovered previously unseen behaviors in magic-angle twisted bilayer graphene using terahertz light. As part of this international effort, the research sheds new light on the quantum geometry of this enigmatic material, revealing how the electronic wavefunctions of electrons are shaped by their environment.

Researchers, including members from ML4Q (Stampfer Group), contributed to this work by exploring how terahertz light interacts with twisted bilayer graphene at a level never before observed in quantum transport experiments. By utilizing terahertz light instead of traditional mid-infrared sources, the team uncovered anomalies in electron behavior, even in high-temperature conditions that typically obscure exotic quantum phenomena.

The findings highlight the importance of quantum geometry—the shape and structure of an electron’s wavefunction—which profoundly influences the material’s electronic properties. Through polarization-resolved measurements of the photocurrent generated by terahertz light, the researchers were able to directly probe how electron interactions reshape the quantum geometry of the graphene lattice. The results revealed phenomena previously hidden, such as energy gaps between electron states, which are critical to understanding topological phases and superconductivity in quantum materials.

Publication: Krishna Kumar, R., Li, G., Bertini, R. et al. Terahertz photocurrent probe of quantum geometry and interactions in magic-angle twisted bilayer graphene. Nat. Mater. (2025).
DOI: https://doi.org/10.1038/s41563-025-02180-3

For more details, check out the ICFO press release!