Extreme Magnetoresistance Reveals Unexpected Insulating Phase in a Semimetal

2025-5-21

JPS Hot Topics 5, 026

https://doi.org/10.7566/JPSHT.5.026

This article is on

Insulating Behavior in the Quantum Limit State of Bi_1-xSb_x (x ∼ 0.04) in the Vicinity of Semimetal-Semiconductor Transition
(JPSJ Editors’ Choice)

Yuma Yamaguchi, Takuya Fujita, Yuto Kinoshita, Akiyoshi Yamada, Atsushi Miyake, Ryota Hiraoka, Tatsuma D. Matsuda, Ryo Ninohira, Ryosuke Kurihara, Hiroshi Yaguchi, Yuki Fuseya, and Masashi Tokunaga
J. Phys. Soc. Jpn. 94, 043701 (2025) .

We discovered an anomalous quantum state in which electric conduction exhibits a gapped behavior exclusively in one direction, in the quantum limit of the BiSb alloy under strong magnetic fields.

We can realize a quantum limit in extremely strong magnetic fields, where all charge carriers in metals occupy only the lowest-energy quantum state. Further increases in the magnetic field suppress the kinetic degrees of freedom of the carriers and incorporate electron correlation effects. Understanding the types of quantum states emerging from strongly correlated three-dimensional materials in the quantum limit remains a significant challenge, as magnetic fields exceeding 10,000 T are required to reach this state in conventional metals.

We investigated the semimetallic BiSb alloy to explore this novel quantum state in the quantum limit. Applying magnetic fields perpendicular to the three-fold rotational axis of this material reduces the overlap between the conduction and valence bands, inducing a semimetal-semiconductor transition at a specific magnetic field. Consequently, we can delve deeper into the quantum limit in fields slightly below this transition field. Our transverse magnetoresistance measurements (with current perpendicular to the magnetic field) exhibited clear quantum oscillations, indicating that the material remains semimetallic and reaches the quantum limit for both electron and hole carriers in magnetic fields up to 60 T. In contrast, the longitudinal magnetoresistance (with current parallel to the magnetic field) showed steep increase at magnetic fields above 30 T. Analysis of the transport data revealed a gap of a few meV only during conduction along the magnetic field, with no corresponding gap observed in the energy diagram calculated for single-particle states that neglect electron correlation effects.

Further investigations are required to clarify the origin of this anomalous insulating state in the quantum limit. Similar anisotropic insulating behaviors have recently been observed in several topological semimetals under high magnetic fields. It would be interesting to explore the tunable electron correlation effects, influenced by magnetic fields, in topological semimetals.

(Written by Masashi Tokunaga on behalf of all authors.)

Insulating Behavior in the Quantum Limit State of Bi_1-xSb_x (x ∼ 0.04) in the Vicinity of Semimetal-Semiconductor Transition
(JPSJ Editors’ Choice)