The growing charge-density-wave order in CuTe lightens and speeds up electrons

I-Ta Wang; Ta-Lei Chou; Chih-En Hsu; Zhujialei Lei; Li-Min Wang; Ping-Hui Lin; Chih-Wei Luo; Chun-Wei Chen; Chia-Nung Kuo; Chin Shan Lue; Cheng-Hsuan Chen; Hung-Chung Hsueh; Ming-Wen Chu

doi:10.1038/s41467-024-53653-z

The growing charge-density-wave order in CuTe lightens and speeds up electrons

Nat Commun. 2024 Oct 29;15(1):9345. doi: 10.1038/s41467-024-53653-z.

Authors

I-Ta Wang^#^{1

2

3

4}, Ta-Lei Chou^#^{1

2}, Chih-En Hsu⁵, Zhujialei Lei⁶, Li-Min Wang⁶, Ping-Hui Lin⁷, Chih-Wei Luo⁸, Chun-Wei Chen^{3

4

9}, Chia-Nung Kuo¹⁰, Chin Shan Lue^{10

11

12}, Cheng-Hsuan Chen¹, Hung-Chung Hsueh¹³, Ming-Wen Chu^{14

15}

Affiliations

¹ Center for Condensed Matter Sciences, National Taiwan University, Taipei, 10617, Taiwan.
² Center of Atomic Initiative for New Materials, National Taiwan University, Taipei, 10617, Taiwan.
³ International Graduate Program of Molecular Science and Technology, National Taiwan University (NTU-MST), Taipei, 10617, Taiwan.
⁴ Molecular Science and Technology Program, Taiwan International Graduate Program (TIGP), Academia Sinica, Taipei, 11529, Taiwan.
⁵ Department of Physics, Tamkang University, New Taipei, 251301, Taiwan.
⁶ Department of Physics, National Taiwan University, Taipei, 10617, Taiwan.
⁷ National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan.
⁸ Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, 30010, Taiwan.
⁹ Department of Materials Science and Engineering, National Taiwan University, Taipei, 10617, Taiwan.
¹⁰ Department of Physics, National Cheng Kung University, Tainan, 70101, Taiwan.
¹¹ Taiwan Consortium of Emergent Crystalline Materials, National Science and Technology Council, Taipei, 10601, Taiwan.
¹² Program on Key Materials, Academy of Innovative Semiconductor and Sustainable Manufacturing, National Cheng Kung University, Tainan, 70101, Taiwan.
¹³ Department of Physics, Tamkang University, New Taipei, 251301, Taiwan. hchsueh@gms.tku.edu.tw.
¹⁴ Center for Condensed Matter Sciences, National Taiwan University, Taipei, 10617, Taiwan. chumingwen@ntu.edu.tw.
¹⁵ Center of Atomic Initiative for New Materials, National Taiwan University, Taipei, 10617, Taiwan. chumingwen@ntu.edu.tw.

^# Contributed equally.

Abstract

Charge density waves (CDWs) are pervasive orders in solids that usually enhance the effective mass (m*) and reduce the Fermi velocity ( $v_{F}$ ) of carriers. Here, we report on the inverse - a reduced m* and an enhanced $v_{F}$ correlated with the growth of the CDW order in CuTe with gapped, practically linearly dispersing bands - reminiscent of emergent CDW-gapped topological semimetals. Using momentum-dependent electron energy-loss spectroscopy (q-EELS), we simultaneously capture m* and $v_{F}$ of the CDW-related, practically linearly dispersing electrons by plasmon dispersions across the transition (335 K, T_CDW), with m* of 0.28 m₀ (m₀, the electron rest mass) and $v_{F}$ of ~ 0.005c (c, the speed of light) at 300 K. With the growth of the CDW order-parameter strength toward 100 K, the electrons become lighter and move faster by ~ 20%. Thorough inspection below T_CDW unveils the essential role of the increasing opening of the CDW gap. CuTe is a rich platform for the exploration of CDW/correlation physics with q-EELS established as a useful probe for this type of physics.