Comparison of tunneling spectra for normal and charge density wave states in 1T-TiSe₂

The tunneling spectrum of 1T-TiSe₂ in the charge density wave (CDW) state shows a dip structure below the Fermi level, and it is unclear whether this dip is a CDW gap. Answering this question is important because information regarding the CDW gap estimated from the dip is referred in discussions of the driving mechanism of this CDW. Therefore, we used scanning tunneling microscopy/scanning tunneling spectroscopy to acquire tunneling spectra for the normal and CDW states in TiSe₂ and compared the spectra. Specifically, we measured pure TiSe₂ at 293 K (>T_CDW) and 4.2 K (<T_CDW) and annealed TiSe₂, in which the CDW is suppressed. As a result, we found that the tunneling spectra for the normal states exhibit a dip below the Fermi level similar to the spectrum for the CDW state. These results indicate that the dip itself is not a CDW gap.