Redox-Coupled Structural Distortions in the Quasi-1-Dimensional Au2M1-xP2 System

Symmetry and Fermi-level filling are two variables that lie at the foundation in investigating topological materials. For example, in the GdSb_xTe_2-x-_δ system, the Sb:Te ratio governs the electron-filling of the band structure, producing a tunable system of structural distortions in its square-net layer. At specific ratios, these distortions retain certain symmetry-protected bands, such as a Dirac node on the Fermi surface, and gap out topologically trivial bands at the Fermi surface. One interest now is to investigate tunable topological structural motifs beyond a square-net of atoms. A one-dimensional (1D) chain of atoms realizes analogous symmetry protected Dirac nodes as the square net. The first part of my presentation expands on previously reported Au₂MP₂(M=Hg, Tl, Pb, and now Bi), which contains a 1D chain of M atoms. Surprisingly, this structure type stabilizes across a difference of four electrons per chain atom, while the Bi analogue also contains a monoclinic polymorph that retains the linear chain of Bi atoms. The second part of my presentation demonstrates the importance of chemical workup in solid state compounds. X-ray and electron diffraction characterizations indicate crystals of the Au₂MP₂ system undergoes a redox-mediated structural distortion whose resulting symmetry and size of supercell depends on the identity of M. Further characterization and computations suggest modulated coordination enviornments as a possible driving force for the distortions. Finally, electronic transport between the modulated and unmodulated compounds are compared. As a result of these insights, nearly isolated 1D chains can be further probed in differing chemical environments.