Scientists have unveiled a cutting-edge quantum microscope that allows them to observe how electrons interact with strange atomic vibrations in twisted graphene, including a newly revealed “phason.”
This phenomenon could help explain mysterious behaviors like superconductivity in materials rotated to the “magic angle.” The breakthrough, made possible by operating the microscope at cryogenic temperatures, marks a major leap in studying quantum materials and opens the door to future discoveries in computing and electronics.
Breakthrough Tool for Quantum Exploration
In a recent study published in Nature, scientists at the Weizmann Institute unveiled a powerful new instrument for probing quantum materials: the cryogenic Quantum Twisting Microscope (QTM). With this advanced tool, researchers have, for the first time, observed how electrons interact with a rare atomic vibration, known as a phason, in twisted layers of graphene.
This discovery provides fresh insight into two puzzling phenomena seen in these materials: superconductivity and strange metallicity, which arise when the graphene layers are rotated to a specific “magic angle.”
Electron-Phonon Coupling and Superconductivity
A material’s basic properties are shaped by the behavior of its fundamental particles. Electrons influence electrical resistance, while phonons, vibrations in the atomic lattice, carry heat. When these two interact, entirely new behaviors can emerge. One of the most fascinating outcomes is when phonons help electrons form pairs, allowing electricity to flow without resistance, a hallmark of superconductivity. Despite its importance, it has been very difficult to measure how electrons couple to specific phonon modes. The new QTM now makes that possible.
Origins of the Quantum Twisting Microscope
Two years ago, a team of researchers from the Weizmann Institute of Science, led by Prof. Shahal Ilani, developed the Quantum Twisting Microscope. This microscope uses an atomically-thin van-der-Waals material at its tips as a quantum interferometer, enabling direct measurement of the electronic wavefunctions within a quantum material. With their original QTM, operating at room temperature, they were able to image the electronic spectrum of various materials.
Imaging Phonons at Cryogenic Temperatures
Now, creating a QTM that works at cryogenic temperatures, the team discovered that it can also image phonons with unprecedented precision. The new QTM employs an inelastic process, where electrons tunneling between two atomically-thin layers emit a phonon whose energy and momentum are controlled by adjusting the voltage bias and twist angle between the layers. By systematically tuning these parameters, they could map the complete phonon energy spectrum of the material under investigation.
Mapping Electron-Phonon Interactions
“Our technique not only measures the phonon spectrum but also quantifies how strongly electrons couple to each phonon mode,” says Dr. John Birkbeck, a lead author of this study. “Materials host numerous phonon modes, each can have a wide range of momenta. Our microscope quantitatively reveals how electrons interact with each mode individually, providing unprecedented insight into electron-phonon dynamics.”
Discovery of the “Phason” Mode in Graphene
Applying this novel technique to twisted bilayer graphene yielded a surprising discovery: a unique low-energy vibration known as a “phason,” whose coupling to electrons grows stronger as the graphene layers approach the magic angle. This behavior had never been observed before and suggests that phasons may play a key role in the strange metal behavior and superconductivity observed in this system.
Beyond Phonons: Probing New Quantum Modes
“Our method extends far beyond phonons,” adds Jiewen Xiao, another lead author on the study. “It can detect any excitation coupled to tunneling electrons, opening exciting avenues to explore other collective modes such as plasmons, magnons, spinons and other goldstone modes across a diverse range of quantum materials.”
“This study makes us feel optimistic about future discoveries,” says Alon Inbar, a fellow lead author. “Significant progress in our understanding of these fundamental modes in quantum materials will come shortly.”
With this significant expansion in its capabilities, the QTM is poised to become a transformative instrument for quantum materials research. Its unique ability to probe both electronic states and collective excitations paves the way for discoveries relevant to quantum computing, sensing technologies, and future quantum electronic devices.
Reference: “Quantum twisting microscopy of phonons in twisted bilayer graphene” by J. Birkbeck, J. Xiao, A. Inbar, T. Taniguchi, K. Watanabe, E. Berg, L. Glazman, F. Guinea, F. von Oppen and S. Ilani, 23 April 2025, Nature.
DOI: 10.1038/s41586-025-08881-8
