Scanning Tunneling Microscopy and Spectroscopy (STM/S) Reveals Small Energy Gap of CrBr₃

CrBr₃ is a 2D van der Waals magnetic material. Despite the great attention on the magnetic properties, the electronic properties of the CrBr₃ are relatively unexplored. The energy gap of CrBr₃ is believed to be in the range of 1.68-2.1 eV, based on the optical measurements. Density fluctuation theory (DFT) calculations show even higher deviation in the energy gap. These controversies have indicated that the energy gap of CrBr₃ is not well studied. Here, we present results from scanning tunneling microscopy and spectroscopy (STM/S) on a defect free surface that is confirmed by atomic resolution topography, having much smaller energy gap (0.57 ± 0.04eV) in thick flake. The multi-peak dI/dV spectrum measured at 77K represents the energies of high density of states (DOS). The energy difference between the conduction band-valance band peak pairs in multi-peak spectrum agrees well with the reported optical transitions further confirming that the measured peaks are intrinsic to CrBr₃. DFT calculations with U = 5 eV and J = 3 eV reproduce this energy gap. Finally, the mono- and bi-layer flake shows edge degradation due to ~15 minutes of air exposure during sample transfer. These observations of energy states provide important information towards the fundamental understanding of CrBr₃.