Small energy gap revealed in CrBr by scanning tunneling spectroscopy

• Published in: Physical chemistry chemical physics : PCCP 2021-02, Vol.23 (5), p.3225-3232
• Main Authors: Baral, Dinesh, Fu, Zhuangen, Zadorozhnyi, Andrei S, Dulal, Rabindra, Wang, Aaron, Shrestha, Narendra, Erugu, Uppalaiah, Tang, Jinke, Dahnovsky, Yuri, Tian, Jifa, Chien, TeYu
• Format: Article
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d0cp05633b

CrBr 3 is a layered van der Waals material with magnetic ordering down to the 2D limit. For decades, based on optical measurements, it is believed that the energy gap of CrBr 3 is in the range of 1.68-2.1 eV. However, controversial results have indicated that the band gap of CrBr 3 is possibly smaller than that. An unambiguous determination of the energy gap is critical to the correct interpretations of the experimental results of CrBr 3 . Here, we present the scanning tunneling microscopy and spectroscopy (STM/S) results of CrBr 3 thin and thick flakes exfoliated onto highly ordered pyrolytic graphite (HOPG) surfaces and density functional theory (DFT) calculations to reveal the small energy gap (peak-to-peak energy gap to be 0.57 ± 0.04 eV; or the onset signal energy gap to be 0.29 ± 0.05 eV from d I /d V spectra). Atomic resolution topography images show the defect-free crystal structure and the d I /d V spectra exhibit multiple peak features measured at 77 K. The conduction band - valence band peak pairs in the multi-peak d I /d V spectrum agree very well with all reported optical transitions. STM topography images of mono- and bi-layer CrBr 3 flakes exhibit edge degradation due to short air exposure (∼15 min) during sample transfer. The unambiguously determined small energy gap settles the controversy and is the key in better understanding CrBr 3 and similar materials. Using scanning tunneling spectroscopy (d I /d V ) measurements, small energy gap was revealed in CrBr 3 flakes.