Charge density wave in a band insulator

Charge-density-wave implies a periodic modulation of the charge density. Typically observed in metallic systems, charge-density-wave arise from Fermi surface instabilities, resulting in the total or partial gapping of the Fermi surface. Here, we present experimental evidence for a charge-density-wave state emerging in a band insulator which has no Fermi surface. The bulk and surface of our material platform, $${\rm{\alpha }}$$-Bi4Br4, is gapped over the entire Brillouin zone. Through topographic and spectroscopic imaging at low temperatures, we unveil an unexpected unidirectional charge modulation in $${\rm{\alpha }}$$-Bi4Br4, breaking the lattice translation symmetry. The charge-density-wave develops at temperatures below 40 K and adds an energy gap atop the existing insulating gap of $${\boldsymbol{\alpha }}$$-Bi4Br4. Furthermore, our transport measurements reveal nonlinear electrical conduction, a phenomenon conventionally associated with the sliding or phason mode of incommensurate charge-density-waves. These unusual observations represent a different type of charge-density-wave. Charge density waves typically occur in metallic systems. Here, the authors show evidence of a charge density wave state in a band insulator state in α-Bi4Br4.

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Publication Details

Journal
Nature Communications
Published
2026-06-08
DOI
https://doi.org/10.1038/s41467-026-71570-1
Primary Topic
Quantum and electron transport phenomena
Type
article
Field-Weighted Citation Impact
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article

Charge density wave in a band insulator

Tyler A. Cochran, Nana Shumiya, Maksim Litskevich, Kouta Dagnino et al.
Nature Communications
Quantum and electron transport phenomena
article

Charge density wave in a band insulator

Tyler A. Cochran, Nana Shumiya, Maksim Litskevich, Kouta Dagnino, Xian P. Yang, Md Shafayat Hossain, Jia-Xin Yin, Wenhao Liu, Titus Neupert, Nikhil Dhale, Bing Lv, M. Zahid Hasan, Fan Zhang, Zijia Cheng, Yongkai Li, Yugui Yao, Byunghoon Kim, Yu-Xiao Jiang, Qi Zhang, Zhiwei Wang, Yuqi Zhang, Chao Lei, Luis Balicas
article en

Abstract

Charge-density-wave implies a periodic modulation of the charge density. Typically observed in metallic systems, charge-density-wave arise from Fermi surface instabilities, resulting in the total or partial gapping of the Fermi surface. Here, we present experimental evidence for a charge-density-wave state emerging in a band insulator which has no Fermi surface. The bulk and surface of our material platform, $${\rm{\alpha }}$$-Bi4Br4, is gapped over the entire Brillouin zone. Through topographic and spectroscopic imaging at low temperatures, we unveil an unexpected unidirectional charge modulation in $${\rm{\alpha }}$$-Bi4Br4, breaking the lattice translation symmetry. The charge-density-wave develops at temperatures below 40 K and adds an energy gap atop the existing insulating gap of $${\boldsymbol{\alpha }}$$-Bi4Br4. Furthermore, our transport measurements reveal nonlinear electrical conduction, a phenomenon conventionally associated with the sliding or phason mode of incommensurate charge-density-waves. These unusual observations represent a different type of charge-density-wave. Charge density waves typically occur in metallic systems. Here, the authors show evidence of a charge density wave state in a band insulator state in α-Bi4Br4.

Nature Communications
Beijing Institute of Technology (CN), California NanoSystems Institute (US), Baylor University (US), University of California, Los Angeles (US), The University of Texas at Dallas (US), Princeton University (US), University of Zurich (CH), Beijing Institute of Optoelectronic Technology (CN), Beijing Academy of Quantum Information Sciences (CN), Oklahoma State University Center for Health Sciences (US), Wuxi Institute of Technology (CN), The University of Texas at Austin (US)
Affordable and clean energy
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Quantum and electron transport phenomena
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