Observation of Charge Density Wave in Layered Hexagonal Cu$_{1.89}$Te Single Crystal
Wenshuai Gao1†, Zheng Chen2,4†, Wensen Wei2, Chao Yan3, Shasha Wang2,4, Jin Tang2, Ranran Zhang2, Lixun Cheng1, Pengfei Nan1, Jie Wang2,4, Yuyan Han2, Chuanying Xi2, Binghui Ge1, Lin He3, Haifeng Du1,2, Wei Ning2, Xiangde Zhu2*, and Mingliang Tian2,5*
1Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, China 2Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, China 3Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, Beijing 100875, China 4Department of physics, University of Science and Technology of China, Hefei 230026, China 5School of Physics and Optoelectronics Engineering, Anhui University, Hefei 230601, China
Abstract：We report comprehensive transport, electron microscopy and Raman spectroscopy studies on transition-metal chalcogenides Cu$_{1.89}$Te single crystals. The metallic Cu$_{1.89}$Te displays successive metal-semiconductor transitions at low temperatures and almost ideal linear MR when magnetic field up to 33 T. Through the electron diffraction patterns, the stable room-temperature phase is identified as a $3 \times 3\times 2$ modulated superstructure based on the Nowotny hexagonal structure. The superlattice spots of transmission electron microscopy and scanning tunneling microscopy clearly show the structural transitions from the room-temperature commensurate I phase, named as C-I phase, to the low temperature commensurate II (C-II) phase. All the results can be understood in terms of charge density wave (CDW) instability, yielding intuitive evidences for the CDW formations in Cu$_{1.89}$Te. The additional Raman modes below room temperature further reveal that the zone-folded phonon modes may play an important role on the CDW transitions. Our research sheds light on the novel electron features of Cu$_{1.89}$Te at low temperature, and may provide potential applications for future nano-devices.
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2023, Vol. 40 
