The exfoliation of NbSe 2 I 2 single crystals was carried under ambient atmosphere. We used 3M Scotch tape to cleave a crystal around 10 times and exfoliated the flake onto a 285 nm/550 µm SiO 2 /Si wafer (Nova wafers Inc.). After exfoliation, the sample was kept in a N 2 glove box until optical spectroscopy measurements. Raman spectroscopy was carried out in a Nanophoton Raman 11 spectrometer under ambient atmosphere with a 532 nm laser and optical grating with 2400 lines per mm. The laser spot size is estimated to be 0.7 µm, with an intensity of 0.1 mW and 10 s count time. After obtaining the raw spectra, a clean silicon wafer was used to calibrate the spectra with the characteristic Raman resonance peak of silicon at 520 cm -1 .