Discovery of the Reverse Quantum Limit

Published July 16, 2024

A phase diagram categorizing material behavior under high magnetic fields.

An analogue of the quantum limit in metals, where very strong magnetic fields confine electrons to the lowest Landau level, has been discovered in the Kondo insulator YbB₁₂. In an insulator, the Landau level filling is shown to take place in the reverse upon closing the gap with a magnetic field.

What did scientists discover?

The "quantum limit" occurs when strong magnetic fields trap electrons in a single state in metals. A similar effect, called the "reverse quantum limit," has been found in insulators. This was discovered by studying the material YbB₁₂ at low temperatures and high magnetic fields.

Why is this important?

Unconventional electronic phases help scientists explore and test their understanding of condensed-matter systems. These phases are expected to appear in metals under strong magnetic fields, especially if the electrons interact strongly with each other. However, other effects often dominate in such metals, making these phases hard to study. We've found that this "quantum-limit-physics" can happen in strongly-correlated insulators instead. This "reverse quantum limit" in insulators is similar to the quantum limit in metals, but with magnetic fields causing electronic states to behave in the opposite way.

This discovery shows that strongly-correlated insulators are the best platform to explore unusual electronic phases in the "reverse" quantum limit. It also offers new insights into the strange behavior of YbB₁₂, which blurs the usual line between metals and insulators.

Who did the research?

C.A. Mizzi¹, S.K. Kushwaha^1,2,3,4, P.F.S. Rosa⁵, W.A. Phelan^3,4,6, D.C. Arellano⁶, L.A. Pressley^3,4,7, T.M. McQueen^2,3,7, M.K. Chan¹, N. Harrison¹

¹National High Magnetic Field Laboratory, Los Alamos National Laboratory; ²Institute for Quantum Matter, The Johns Hopkins University; ³Department of Chemistry, The Johns Hopkins University; ⁴PARADIM, The Johns Hopkins University; ⁵MPA-Q, Los Alamos National Laboratory; ⁶MST-16, Los Alamos National Laboratory; ⁷Department of Materials Science and Engineering, The Johns Hopkins University

Why did they need the MagLab?

The unique magnet systems available at the NHMFL’s Pulsed Field Facility were integral to this work because much of the rich physics exhibited by YbB₁₂ requires extraordinarily large magnetic fields to observe: quantum oscillations begin around 35T and the insulator-metal transition extends to nearly 55T! The 65T short-pulse and 75T duplex magnets at the Pulsed Field Facility were crucial to access these regimes in YbB₁₂.

Details for scientists

View or download the expert-level Science Highlight, Discovery of the Reverse Quantum Limit
Read the full-length publication, The reverse quantum limit and its implications for unconventional quantum oscillations in YbB₁₂, in Nature Communications

Funding

This research was funded by the following grants: G.S. Boebinger (NSF DMR-2128556); T.M. McQueen (NSF DMR-1539918, DOE DE-SC0019331); N. Harrison (DOE “Science of 100 Tesla”)

For more information, contact Neil Harrison.