Electronic Phase Transition in Layered Materials 1T-TaSxSe2-x Probed by Cryogenic STM/STS
T. Hasegawa
Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsutacho 4259, Midori-ku, Yokohama 226, Japan

O. Shiino, W. Yamaguchi, T. Endo, H. Sugawara and K. Kitazawa
Department of Applied Chemistry, University of Tokyo, Japan Science and Technology Corporation, Hongo 7-3-1, Bunkyo-ku, Tokyo 113, Japan
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A metal-insulator transition, Mott transition, in layered materials 1T-TaSxSe2-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-TaS2, 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.
DOI: 10.12693/APhysPolA.93.297
PACS numbers: 71.30.+h, 71.20.-b