A metal-insulator transition, Mott transition, in layered materials 1T-TaS_{x}Se_{2-x} was investigated by cryogenic scanning tunneling microscopy/ spectroscopy. At 77 K, tunneling spectra in the insulating phase showed a conduction band with almost half filling, which becomes narrower as x decreases. Around the transition point x≈1.4 at 77 K, we observed a sign of gap opening without an overshooting peak at zero bias, supporting the Mott localization picture in which a carrier number vanishes at the transition point. From the site-specified scanning tunneling spectroscopy measurements, furthermore, electrons were found to localize at the charge density wave crest positions. In 1T-TaS_{2}, we have also found that both metallic and insulating phases coexist in a nanometer scale just above the transition temperature, 180 K. >From the minimum size of the insulating region, the coherence length of Mott insulating state was evaluated to be≈5 nm.
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