Quantum twisting microscopy of phonons in twisted bilayer graphene

J. Birkbeck; J. Xiao; A. Inbar; T. Taniguchi; K. Watanabe; E. Berg; L. Glazman; F. Guinea; F. von Oppen; S. Ilani

doi:10.1038/s41586-025-08881-8

Journal article Quantum twisting microscopy of phonons in twisted bilayer graphene

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J. Birkbeck, J. Xiao, A. Inbar, T. Taniguchi, K. Watanabe, E. Berg, L. Glazman, F. Guinea, F. von Oppen, S. Ilani. Quantum twisting microscopy of phonons in twisted bilayer graphene. Nature. 2025, 641 (8062), 345-351. https://doi.org/10.1038/s41586-025-08881-8

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The coupling between electrons and phonons is one of the fundamental interactions in solids, underpinning a wide range of phenomena such as resistivity, heat conductivity, and superconductivity. However, direct measurements of this coupling for individual phonon modes remains a significant challenge. In this work, we introduce a novel technique for mapping phonon dispersions and electron phonon coupling (EPC) in van der Waals materials. By generalizing the quantum twisting microscope1 to cryogenic temperatures, we demonstrate its capability to map not only electronic dispersions via elastic momentum-conserving tunnelling, but also phononic dispersions through inelastic momentum-conserving tunnelling. Crucially, the inelastic tunnelling strength provides a direct and quantitative measure of the momentum and mode resolved EPC. We use this technique to measure the phonon spectrum and EPC of twisted bilayer graphene (TBG) with twist angles larger than 6°. Surprisingly, we find that unlike standard acoustic phonons, whose coupling to electrons diminishes as their momentum goes to zero, TBG exhibits a low energy mode whose coupling increases with decreasing twist angle. We show that this unusual coupling arises from the modulation of the inter-layer tunnelling by a layer-antisymmetric “phason” mode of the moiré system. The technique demonstrated here opens the way for probing a large variety of other neutral collective modes that couple to electronic tunnelling, including plasmons2, magnons3 and spinons4 in quantum materials.

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