University of Illinois Urbana-Champaign

Disorder and diffuse scattering in single-chirality (TaSe4)2I crystals

Christensen, Jacob Andrew

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https://hdl.handle.net/2142/122172

Description

Title
Disorder and diffuse scattering in single-chirality (TaSe4)2I crystals
Author(s)
Christensen, Jacob Andrew
Issue Date
2023-12-05
Director of Research (if dissertation) or Advisor (if thesis)
Shoemaker, Daniel P
Department of Study
Materials Science & Engineerng
Discipline
Materials Science & Engr
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
  • Charge density waves
  • Peierls transition
  • Topological materials
  • Pump-probe spectroscopy
  • Scanning transmission electron microscopy
  • X-ray diffraction
  • Chiral symmetry
  • Lattice modeling
Abstract
The quasi-one-dimensional chiral compound (TaSe4)2I has been extensively studied as a prime example of a topological Weyl semimetal. Upon crossing its phase transition temperature T_CDW ≈ 263 K, (TaSe4)2I exhibits incommensurate charge density wave (CDW) modulations described by the well-defined propagation vector ∼(0.05, 0.05, 0.11), oblique to the TaSe4 chains. Although optical and transport properties greatly depend on chirality, there is no systematic report about chiral domain size for (TaSe4)2I. In this study, our single-crystal scattering refinements reveal a bulk iodine deficiency, and Flack parameter measurements on multiple crystals demonstrate that separate (TaSe4)2I crystals have uniform handedness, supported by direct imaging and helicity dependent THz emission spectroscopy. Our single-crystal X-ray scattering and calculated diffraction patterns identify multiple diffuse features and create a real-space picture of the temperature-dependent (TaSe4)2I crystal structure. The short-range diffuse features are present at room temperature and decrease in intensity as the CDW modulation develops. These transverse displacements, along with electron pinning from the iodine deficiency, help explain why (TaSe4)2I behaves as an electronic semiconductor at temperatures above and below T_CDW, despite a metallic band structure calculated from density functional theory of the ideal structure.
Graduation Semester
2023-12
Type of Resource
Thesis
Handle URL
https://hdl.handle.net/2142/122172
Copyright and License Information
Copyright 2023 Jacob Andrew Christensen

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