University of Michigan researchers have confirmed that the Kondo insulator ytterbium boride (YbB12) exhibits intrinsic quantum oscillations that originate in its bulk, not just at the surface. New measurements at the National Magnetic Field Laboratory provide direct thermodynamic evidence linking the oscillations to quasiparticle states inside the material. The effect appears only at very high fields (~35 Tesla), far above typical MRI strengths, and practical applications are not yet known. The finding challenges existing theories and may inspire new research into strongly correlated electron systems.
Strange Quantum Signals Inside an Insulator: YbB12 Shows Bulk Oscillations at 35 Tesla
University of Michigan researchers have confirmed that the Kondo insulator ytterbium boride (YbB12) exhibits intrinsic quantum oscillations that originate in its bulk, not just at the surface. New measurements at the National Magnetic Field Laboratory provide direct thermodynamic evidence linking the oscillations to quasiparticle states inside the material. The effect appears only at very high fields (~35 Tesla), far above typical MRI strengths, and practical applications are not yet known. The finding challenges existing theories and may inspire new research into strongly correlated electron systems.
07:53 AM, 11/19/2025Science
Researchers at the University of Michigan report new thermodynamic evidence that the Kondo insulator ytterbium boride (YbB12) produces quantum oscillations that originate in its bulk rather than only at the surface. The result, published in Physical Review Letters, strengthens earlier hints of this unusual behavior and raises fresh questions about the electronic nature of Kondo insulators.
In conventional materials, quantum oscillations typically reflect mobile charge carriers in a metal. YbB12 is unusual because its bulk behaves like an electrical insulator while its surface can be conductive. In 2018, Lu Li and colleagues observed quantum oscillations under very strong magnetic fields and suggested the signals might arise from the material’s interior—contradicting expectations based on well-known topological insulators. Independent experiments from other groups, including work at the University of Cambridge, had produced data consistent with this puzzling picture.
To resolve whether the oscillations are intrinsic and truly bulk-derived, Li’s team performed high-precision measurements using the ultra-high-field magnets at the National Magnetic Field Laboratory in Tallahassee. The new measurements provide direct thermodynamic evidence linking the observed thermal signatures to the same quasiparticle states responsible for the oscillations, indicating the effect is intrinsic to YbB12’s insulating interior.
"The community has not yet reached a consensus on fundamental questions about the quantum oscillations; debates persist about whether the oscillations originate from the surface or the bulk and whether they are intrinsic or extrinsic," the authors write, emphasizing the need for thermodynamic confirmation.
The experiments show the bulk oscillatory behavior appears only under extremely large magnetic fields—around 35 Tesla. For context, a typical medical MRI operates near 1 Tesla, so these conditions are far beyond everyday laboratory or clinical equipment. The high-field threshold means the phenomenon is not readily exploitable with current, low-field technologies.
Li and collaborators acknowledge that immediate applications are unclear. Although surface-conducting topological insulators have spurred new quantum device ideas, a material that shows quantum oscillations originating in an insulating bulk presents a novel and unresolved physical scenario. The team likens this to historical cases—such as early work on lasers—where initially mysterious phenomena later became technologically transformative.
Beyond potential applications, the result is important for fundamental condensed-matter physics: it challenges our understanding of how strongly correlated electrons can produce exotic quasiparticles and mixed insulating/metallic behavior. Future theoretical and experimental work will be needed to identify the microscopic origin of the bulk quasiparticles and to explore whether related materials exhibit similar effects under accessible conditions.