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1995 Fiscal Year Final Research Report Summary

Direct observations of order parameters and microscopic analysis on phase transition

Research Project

Project/Area Number 06452056
Research Category

Grant-in-Aid for General Scientific Research (B)

Allocation TypeSingle-year Grants
Research Field 固体物性Ⅱ(磁性・金属・低温)
Research InstitutionThe University of Tokyo

Principal Investigator

HASEGAWA Tetuya  The University of Tokyo, Graduate Course of Applied Chemistry, Lecturer, 大学院・工学系研究科, 講師 (10189532)

Project Period (FY) 1994 – 1995
KeywordsSTM / tunneling spectroscopy / local density of states / CDW / Mott localization
Research Abstract

I proposed the atomic site tunneling (AST) spectroscopy which can obtained the tunneling spectrum specified on each atomic site by combining the scanning tunneling microscopy and tunneling spectroscopy Furthermore, I have succeeded in building up an AST apparatus by improving the mechanical strength of STM head and the electronics. As a model material suitable to the AST measurement, I selected 1T-Ta (S,Se)_2 system, which forms charge density waves below room temperature, and I have demonstrated the performance of AST measurements. In TaS_2, the AST data at room temperature showed slight site dependence, i.e., the tunneling spectra on the crest of CDW is rather metallic in comparison with those at the bottom of CDW.However, the over-all feature of the tunneling spectrum is quantitatively consistent with the band calculation. At77K,in contrast, the obtained tunneling spectra clearly shows a gap structure, and two conductance peaks at the gap edge is enhanced simultaneously on the crest of CDW.This implies that the density of states was transferred from the bottom to crest of CDW.The present tunneling result is a strong evidence for the Mott localization where electrons are localized due to the Coulomb interaction. In TaSe_2, I have not found the gap structure even at low temperatures. Namely, the band picture is essentially valid in this material. By replacing Se by S up to 1 : 1, the tunneling spectra suddenly varied, being consistent with the transport data. For Mott transition, there are two categories, i.e., effective mass diverges, or carrier concentration decreases to zero. I have not observed the zero bias conductance peak expected in the former case, suggesting the former mechanism.

  • Research Products

    (10 results)

All Other

All Publications (10 results)

  • [Publications] T. Hasegawaら: ""Spatial variations of local density of states modified by CDWs in 1T-TaS_<2-x>Se_x"" Surf. Sci.314. 269-274 (1994)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] J. -J. Kimら: ""Site-Specified Tunneling Spectroscopy of Local Density of States in Charge-Density-Wave State of 1T-TaSe_2 at 77K"" Phys. Rev. B. 50. 4958-4961 (1994)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] J. -J. Kimら: ""Observation of Mott Localization Gap Using Low Temperature Scanning Tunneling Microscopy in Commensurate 1T-TaS_2"" Phys. Rev. Lett.73. 2103-2106 (1994)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] J. -J. Kimら: ""Observation of Spatial Variations of Local Density of States in Charge Density Wave State of 1T-TaSe_2 at 77K"" Synthetic Metals. 70. 1271-1272 (1995)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] J. -J. Kimら: ""Site-Specified Tunneling Spectroscopy on Commensurate 1T-TaS_2"" Synthetic Metals. 70. 1273-1274 (1995)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] T.Hasegawa et al.: "Spatial variations of local density of states modified by CDW_s in 1T-TaS_<2-x> Se_x" Surf.Sci.314. 269-274 (1994)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] J.-J.Kim et al.: "Site-Specified Tunneling Spectroscopy of Local Density of States in Charge-Density-Wave State of 1T-TaSe2 at 77K" Phys.Rev.B. 50. 4958-4961 (1994)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] J.-J.Kim et al.: "Observation of Mott Localization Gap Using Low Temperature Scanning Tunneling Microscopy in Commensurate 1T-TaS_2" Phys.Rev.Lett.73. 2103-2106 (1994)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] J.-J.Kim et al.: "Observation of Spatial Variations of Local Density of States in Charge Density Wave State of 1T-TaSe_2 at 77K" Synthetic Metals. 70. 1271-1272 (1995)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] J.-J.Kim et al.: "Site-Specified Tunneling Spectroscopy on Commensurate 1T-TaS_2" Synthetic Metals. 70. 1273-1274 (1995)

    • Description
      「研究成果報告書概要(欧文)」より

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Published: 1997-03-04  

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