Charge density wave in a band insulator

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

doi:10.1038/s41467-026-71570-1

Charge density wave in a band insulator

Md Shafayat Hossain^*
, Wenhao Liu
, Yuqi Zhang
, Qi Zhang
, Chao Lei
, Nana Shumiya
, Kouta Dagnino
, Maksim Litskevich
, Yu Xiao Jiang
, Jia Xin Yin
, Nikhil Dhale
, Zijia Cheng
, Byunghoon Kim
, Yongkai Li
, Tyler A. Cochran
, Xian P. Yang
, Fan Zhang
, Yugui Yao
, Zhiwei Wang^*
, Bing Lv^*

Titus Neupert, Luis Balicas, M. Zahid Hasan^*

^*Corresponding author for this work

School of Physics

University of California at Los Angeles
Princeton University
University of California
University of Texas at Dallas
Beijing Institute of Technology
University of Texas at Austin
University of Zurich
Baylor University

Research output: Contribution to journal › Article › peer-review

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, α-Bi₄Br₄, is gapped over the entire Brillouin zone. Through topographic and spectroscopic imaging at low temperatures, we unveil an unexpected unidirectional charge modulation in α-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 α-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.

Original language	English
Article number	7723
Journal	Nature Communications
Volume	17
Issue number	1
DOIs	https://doi.org/10.1038/s41467-026-71570-1
Publication status	Published - Dec 2026

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Hossain, M. S., Liu, W., Zhang, Y., Zhang, Q., Lei, C., Shumiya, N., Dagnino, K., Litskevich, M., Jiang, Y. X., Yin, J. X., Dhale, N., Cheng, Z., Kim, B., Li, Y., Cochran, T. A., Yang, X. P., Zhang, F., Yao, Y., Wang, Z., ... Hasan, M. Z. (2026). Charge density wave in a band insulator. Nature Communications, 17(1), Article 7723. https://doi.org/10.1038/s41467-026-71570-1

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title = "Charge density wave in a band insulator",

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, α-Bi4Br4, is gapped over the entire Brillouin zone. Through topographic and spectroscopic imaging at low temperatures, we unveil an unexpected unidirectional charge modulation in α-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 α-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.",

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

note = "Publisher Copyright: {\textcopyright} The Author(s) 2026.",

year = "2026",

month = dec,

doi = "10.1038/s41467-026-71570-1",

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Hossain, MS, Liu, W, Zhang, Y, Zhang, Q, Lei, C, Shumiya, N, Dagnino, K, Litskevich, M, Jiang, YX, Yin, JX, Dhale, N, Cheng, Z, Kim, B, Li, Y, Cochran, TA, Yang, XP, Zhang, F, Yao, Y , Wang, Z, Lv, B, Neupert, T, Balicas, L & Hasan, MZ 2026, 'Charge density wave in a band insulator', Nature Communications, vol. 17, no. 1, 7723. https://doi.org/10.1038/s41467-026-71570-1

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T1 - Charge density wave in a band insulator

AU - Hossain, Md Shafayat

AU - Liu, Wenhao

AU - Zhang, Yuqi

AU - Zhang, Qi

AU - Lei, Chao

AU - Shumiya, Nana

AU - Dagnino, Kouta

AU - Litskevich, Maksim

AU - Jiang, Yu Xiao

AU - Yin, Jia Xin

AU - Dhale, Nikhil

AU - Cheng, Zijia

AU - Kim, Byunghoon

AU - Li, Yongkai

AU - Cochran, Tyler A.

AU - Yang, Xian P.

AU - Zhang, Fan

AU - Yao, Yugui

AU - Wang, Zhiwei

AU - Lv, Bing

AU - Neupert, Titus

AU - Balicas, Luis

AU - Hasan, M. Zahid

PY - 2026/12

Y1 - 2026/12

N2 - 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, α-Bi4Br4, is gapped over the entire Brillouin zone. Through topographic and spectroscopic imaging at low temperatures, we unveil an unexpected unidirectional charge modulation in α-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 α-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.

AB - 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, α-Bi4Br4, is gapped over the entire Brillouin zone. Through topographic and spectroscopic imaging at low temperatures, we unveil an unexpected unidirectional charge modulation in α-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 α-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.

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SN - 2041-1723

VL - 17

JO - Nature Communications

JF - Nature Communications

IS - 1

M1 - 7723

ER -

Charge density wave in a band insulator

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