Short-range charge density wave order in 2HTaS2

Jaydeep Joshi, Heather M. Hill, Sugata Chowdhury, Christos D. Malliakas, Francesca Tavazza, Utpal Chatterjee, Angela R. Hight Walker, and Patrick M. Vora
Phys. Rev. B 99, 245144 – Published 25 June 2019
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Abstract

2HTaS2 undergoes a charge density wave (CDW) transition at TCDW75 K, however key questions regarding the onset of CDW order remain under debate. In this study, we explore the CDW transition through a combination of temperature and excitation-dependent Raman spectroscopy, angle resolved photoemission spectroscopy (ARPES), and density functional theory (DFT). Below TCDW we identify two CDW amplitude modes that redshift and broaden with increasing temperature and one zone-folded mode that disappears above TCDW. Above TCDW, we observe a strong two-phonon mode that softens substantially upon cooling, which suggests the presence of substantial lattice distortions at temperatures as high as 250 K. This correlates with the ARPES observation of the persistence of a CDW energy gap above TCDW and finite-temperature DFT calculations of the phonon band structure that indicate an instability occurring well above the CDW transition temperature. DFT also provides the atomic displacements of the CDW amplitude modes and reproduces their temperature dependence. From these observations we suggest that short range CDW order exists well above TCDW, which poses new questions regarding the interplay between electronic structure and vibrational modes in layered CDW materials.

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  • Received 21 March 2019
  • Revised 17 May 2019

DOI:https://doi.org/10.1103/PhysRevB.99.245144

©2019 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Jaydeep Joshi1,2, Heather M. Hill3, Sugata Chowdhury4, Christos D. Malliakas5, Francesca Tavazza4, Utpal Chatterjee6, Angela R. Hight Walker3, and Patrick M. Vora1,2,*

  • 1Department of Physics and Astronomy, George Mason University, Fairfax, Virginia 22030, USA
  • 2Quantum Materials Center, George Mason University, Fairfax, Virginia 22030, USA
  • 3Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
  • 4Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
  • 5Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
  • 6Department of Physics, University of Virginia, Charlottesville, Virginia 22904, USA

  • *Corresponding author: pvora@gmu.edu

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Issue

Vol. 99, Iss. 24 — 15 June 2019

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