Revealing the charge density wave caused by Peierls instability in two-dimensional NbSe₂

Yung-Ting Lee^3,2, Po-Tuan Chen³, Zheng-Hong Li^1*, Jyun-Yu Wu¹, Chia-Nung Kuo^4,5, Chin-Shan Lue^4,5, Chien-Te Wu^1,6, Chien-Cheng Kuo⁷, Cheng-Tien Chiang^8,9, Chun-Liang Lin¹, Chi-Cheng Lee^9,10, Hung-Chung Hsueh^9,10, Ming-Chiang Chung^6,11,12

¹Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
²Department of Chemistry, Tamkang University, Tamsui, New Taipei City, Taiwan
³Department of Vehicle Engineering, National Taipei University of Technology, Taipei, Taiwan
⁴Department of Physics, National Cheng Kung University, Tainan City, Taiwan
⁵Taiwan Consortium of Emergent Crystalline Materials, National Science and Technology Council, Taipei, Taiwan
⁶Physics Division, National Center for Theoretical Sciences, Taipei, Taiwan
⁷Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
⁸Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
⁹Department of Physics, Tamkang University, Tamsui, New Taipei City, Taiwan
¹⁰Research Center of X-ray Science, College of Science, Tamkang University, Tamsui, New Taipei City, Taiwan
¹¹Department of Physics, National Chung Hsing University, Taichung, Taiwan
¹²Max Planck Institute for the Physics of Complex Systems, Dresden, Germany

* Presenter:Zheng-Hong Li, email:zhenghongli.sc11@nycu.edu.tw

The formation of a charge density wave (CDW) in two-dimensional (2D) materials caused by Peierls instability is a controversial topic. This study investigates the extensively debated role of Fermi surface nesting in causing the CDW state in 2H-NbSe₂ materials. Four NbSe₂ structures (i.e., normal, stripe, filled, and hollow structures) are identified on the basis of the characteristics in scanning tunneling microscopy images and first-principles simulations. The calculations reveal that the filled phase corresponds to Peierls’ description; that is, it exhibits fully opened gaps at the CDW Brillouin zone boundary, resulting in a drop at the Fermi level in the density of states and the scanning tunneling spectroscopy spectra. The electronic susceptibility and phonon instability in the normal phase indicate that the Fermi surface nesting is triggered by two nesting vectors, whereas the involvement of only one nesting vector leads to the stripe phase. This comprehensive study demonstrates that the filled phase of NbSe₂ can be categorized as a Peierls-instability-induced CDW in 2D systems.

Keywords: Charge density wave, Peierls transition, Scanning tunneling microscopy, Density functional theory