Rearrangement of the Cation (Ta) of 2H-TaSe2 in the Charge Density Wave Phase (CDW): A DFT Study

ORAL

Abstract

Tantalum diselenide (TaSe2), a layered transition-metal dichalcogenide (TMD), is an electronically interesting material because it exhibits several phase transitions with decreasing temperature. As we lower the temperature, the metallic ground state changes first to an incommensurate charge density wave (ICDW) state at ≈ 122 K, then to a commensurate charge density wave (CCDW) state at ≈ 90 K. Using first-principles calculations (DFT), we present the structural changes, band dispersions at the Fermi level and optical properties of bulk 2H-TaSe2 as a function of electronic temperature. We show that CDW phase appears due to the in-plane displacement of Ta atoms, which leads to the formation of well-defined Ta stripes in CDW phases. Our calculations also reveal new Raman modes in the CDW phases, due to displacement of the cation (Ta) as well as to the strong electron-phonon coupling. Comparison with experiments validate our findings as they, too, observed that all these new Raman modes that are very sensitive to temperature and are not observed in the metallic phase at room-temperature.

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Presenters

  • Sugata Chowdhury

    Physical Measurment Division, NIST, NIST -Natl Inst of Stds & Tech, NIST - National Institute of Standards and Technology

Authors

  • Sugata Chowdhury

    Physical Measurment Division, NIST, NIST -Natl Inst of Stds & Tech, NIST - National Institute of Standards and Technology

  • Heather Hill

    Engineering Physics, National Institute of Standards and Technology, National Institute of Standards and Technology, Physical Measurements Laboratory, National Institute of Standards and Technology, Physical Measurment Division, NIST, NIST -Natl Inst of Stds & Tech, NIST - National Institute of Standards and Technology

  • Jeffrey Simpson

    Engineering Physics, National Institute of Standards and Technology, Physics, Towson University, Physics, Astronomy, and GeoSciences, Towson University, Towson University, Department of Physics, Astronomy, and Geosciences, Towson University, Physics, Astronomy, and Geosciences, Towson Univ and NIST

  • Francesca Tavazza

    Mechanical Measurment Division , NIST, NIST -Natl Inst of Stds & Tech, NIST - National Institute of Standards and Technology, Material Measurement Laboratory, National Institute of Standards and Technology

  • Angela Hight Walker

    Engineering Physics, National Institute of Standards and Technology, National Institute of Standards and Technology, NIST - Natl Inst of Stds & Tech, Physical Measurements Laboratory, National Institute of Standards and Technology, Physical Measurment Division, NIST, NIST -Natl Inst of Stds & Tech, Physical Measurement Laboratory, National Institute of Standards and Technology, NIST - National Institute of Standards and Technology, National Institute of Standards and Technology (NIST), National Institute of Standards & Technology