TEMPERATURE-DEPENDENT SCANNING TUNNELING SPECTROSCOPY OF 1T-TAS2

We have studied temperature-dependent tummeling spectroscopy of 1T-TaS 2 from room temperature down to about 40 K. The spectra indicated an a brupt transition from the charge-density-wave-induced broad depletion to an opening of a deep pseudogap within 1 K of the nearly commensurat e to commensurate transition temperature. The measured pseudogap was d eep enough to form localized states at the Fermi level. In contrast to an inverse photoelectron spectroscopy study, our tunneling results in dicate gap structures of two Hubbard subbands resulting from the band splitting of the Ta 5d band due to the electron correlation effect. We have also found an abrupt increase of thermoelectric voltage developi ng between the tip and sample at the transition temperature.