Ann Arbor Times

An international research team led by Lu Li, a physics professor at the University of Michigan, has reported new findings on quantum oscillations in insulators, specifically in the material ytterbium boride (YbB12). Their work, published in Physical Review Letters, provides evidence that these quantum oscillations originate from the bulk of the material rather than just its surface.

Quantum oscillations are typically observed in metals and involve electron behavior that can be influenced by magnetic fields. However, recent studies have shown similar oscillations in insulators—materials not known for conducting heat or electricity. This raised questions about whether such effects stem from surface phenomena or occur throughout the entire material.

Li explained that while many people are interested in practical applications of such discoveries, this finding is notable primarily for its unusual nature. “I would love to claim that there’s a great application, but my work keeps pushing that dream further away,” Li said. “But what we’ve found is still really bizarre and exciting.”

The experiments were conducted using powerful magnetic fields at the National Magnetic Field Laboratory. The research demonstrated that quantum oscillations in YbB12 arise from within the bulk of the compound when subjected to extremely strong magnetic fields—about 35 times stronger than those used in standard MRI machines.

Kuan-Wen Chen, a research fellow at U-M and part of Li’s team, commented on resolving a longstanding question: “For years, scientists have pursued the answer to a fundamental question about the carrier origin in this exotic insulator: Is it from the bulk or the surface, intrinsic or extrinsic? We are excited to provide clear evidence that it is bulk and intrinsic.”

The study included contributions from more than twelve researchers across six institutions in both the United States and Japan. Additional members from U-M involved were graduate students Yuan Zhu, Guoxin Zheng, Dechen Zhang, Aaron Chan and Kaila Jenkins.

Li contextualized their findings as part of what he calls a "new duality"—the idea that materials can behave as both conductors and insulators under certain conditions. He described how previous scientific understanding focused on dualities like wave-particle behaviors but now extends to electronic properties as well. “Effectively, we’re showing that this naive picture where we envisioned a surface with good conduction that’s feasible to use in electronics is completely wrong,” Li said. “It’s the whole compound that behaves like a metal even though it’s an insulator. Unfortunately, this crazy metal behavior only occurs at 35 Tesla—a magnetic field strength that’s about 35 times what’s inside an MRI machine.”

Yuan Zhu added: “Confirming that the oscillations are bulk and intrinsic is exciting. We don’t yet know what kind of neutral particles are responsible for the observation. We hope our findings motivate further experiments and theoretical work.”

The project received funding support from several organizations including the U.S. National Science Foundation, U.S. Department of Energy, Institute for Complex Adaptive Matter, Gordon and Betty Moore Foundation, Japan Society for the Promotion of Science and Japan Science and Technology Agency.