In a groundbreaking development published this week in Nature, researchers at the Weizmann Institute have unveiled an extraordinary advancement in the study of quantum materials — the cryogenic Quantum Twisting Microscope (QTM). This newly engineered instrument has allowed scientists, for the very first time, to directly observe the intricate interplay between electrons and a previously elusive atomic vibration within twisted bilayer graphene. This vibration, coined a “phason,” emerges uniquely when graphene sheets are rotated to a precise “magic angle” and is believed to hold the key to understanding the enigmatic phenomena of superconductivity and strange metallicity in this system.
Materials derive their fundamental characteristics from the dynamic behavior of their constituent particles. Electrons dictate electrical conductivity, while phonons — quantized vibrations of the atomic lattice — govern thermal transport. When these electrons and phonons interact, the resulting coupling can give rise to groundbreaking quantum phenomena. Among the most compelling of these is superconductivity — a state marked by zero electrical resistance — often triggered by phonon-mediated electron pairing. Yet, the difficulty in directly measuring how electrons couple to each individual phonon mode has long impeded deeper insights into these mechanisms.
The original Quantum Twisting Microscope, devised two years ago by the research team led by Professor Shahal Ilani, harnessed the properties of atomically thin van der Waals materials as quantum interferometers at its probe tips. Operating at room temperature, this instrument could image electronic wavefunctions with remarkable spatial resolution, mapping the electronic spectra of diverse quantum materials. However, its capabilities to directly resolve the subtle lattice vibrations remained unattainable — until now.
The newly developed cryogenic QTM operates at ultra-low temperatures, enhancing its sensitivity and heralding a paradigm shift in the imaging of phonons. It exploits an inelastic tunneling process between two atomically-thin layers, where electrons passing through emit phonons with precisely controlled energies and momenta. By finely adjusting the voltage bias and the twist angle between the layers, researchers can systematically tune and scan a wide portion of the phonon energy landscape, mapping its complete spectrum in extraordinary detail.
This precise control and detection method illuminate not only the presence of unique phonon modes but also how strongly electrons couple to each of these modes individually. As Dr. John Birkbeck explains, “Our technique transcends traditional phonon spectroscopy by providing quantitative measurements of the electron-phonon coupling strength at the single-mode level across a broad momentum range.” This affords unprecedented insight into the fundamental dynamics underpinning quantum behavior in advanced materials.
The application of this technique to twisted bilayer graphene led to a remarkable and unforeseen discovery: the identification of a distinctive low-energy collective excitation termed the “phason.” Unlike typical phonons, phasons are associated with the relative sliding motion between the two graphene sheets. Notably, the electron-phason coupling intensifies as the twist angle approaches the celebrated magic angle, a configuration known to produce exotic superconducting and strange metallic phases. This link hints that phasons may be central actors in the emergence of these quantum states.
Beyond phonons and phasons, the versatility of the cryogenic QTM promises to open new investigative frontiers. Co-author Jiewen Xiao highlights that the method is broadly applicable to the detection of any collective excitation that couples to tunneling electrons. This capability positions the microscope as a vital tool to probe plasmons, magnons, spinons, and other Goldstone modes within a variety of quantum materials, dramatically expanding our experimental toolkit for condensed matter physics.
As we increasingly seek to unravel the mysteries of quantum materials, tools like the cryogenic QTM become indispensable. The research team, including lead author Alon Inbar, expresses optimism that this technical innovation will catalyze rapid progress in understanding the intricate coupling mechanisms at play and unlock new quantum phases of matter that have thus far eluded comprehensive experimental observation.
The cryogenic QTM’s dual capacity to image both the electronic states and their coupled collective excitations crucially positions it at the intersection of fundamental research and applied quantum technologies. Insights gleaned from this instrument are anticipated to accelerate advancements in quantum computing, high-precision sensing, and emerging quantum electronic devices, where harnessing such intricate electron-boson interactions is essential.
The full implications of this research are vast and ripple across the fields of material science and condensed matter physics. By enabling mode-selective and momentum-resolved measurements of electron-phonon interactions, the QTM facilitates an unparalleled understanding of superconductivity’s microscopic origins and the exotic metallic states that challenge current physics paradigms. This opens doors to engineering materials with custom quantum properties tailored for future technologies.
In summary, the introduction of the cryogenic Quantum Twisting Microscope marks a quantum leap in our investigative capabilities. Its application to twisted bilayer graphene reveals that phasons, this newly observed quantum vibrational mode, may play an essential role in modulating the quantum phases within these atomically engineered structures. As this technology matures, it stands poised not only to deepen our comprehension of existing quantum phenomena but also to uncover entirely new realms of quantum matter.
With every new measurement facilitated by QTM, we get closer to unraveling the complex tapestry of interactions that dictate the behavior of electrons in quantum materials. The researchers’ exploration foreshadows a new era where detailed spectroscopic mapping of collective modes becomes routine, laying the foundation for discoveries that could redefine our technological landscape.
Subject of Research:
Electron-phonon coupling and collective excitations in twisted bilayer graphene studied via cryogenic Quantum Twisting Microscopy.
Article Title:
Quantum twisting microscopy of phonons in twisted bilayer graphene
News Publication Date:
2025
Web References:
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Keywords
Phonons, Graphene, Basic research, Discovery research, Superconductivity, Low temperature physics, Measuring instruments, Vibration
