Raman spectrum of layered tilkerodeite (Pd2HgSe3) topological insulator: the palladium analogue of jacutingaite (Pt2HgSe3)

Abstract

The layered mineral tilkerodeite (Pd2HgSe3), the palladium analogue of jacutingaite (Pt2HgSe3), is a promising quantum spin hall insulator for low-power nanospintronics. In this context, a fast and reliable assessment of its structure is key for exploring fundamental properties and architecture of new Pd2HgSe3-based devices. Here, we investigate the first-order Raman spectrum in high-quality, single-crystal bulk tilkerodeite, and analyze the wavenumber relation to its isostructural jacutingaite analogue. By using polarized Raman spectroscopy, symmetry analysis, and first-principles calculations, we assigned all the Raman-active phonons in tilkerodeite, unveiling their wavenumbers, atomic displacement patterns, and symmetries. Our calculations used several exchange–correlation functionals within the density functional perturbation theory framework, reproducing both structure and Raman-active phonon wavenumbers in excellent agreement with experiments. Also, it was found that the influence of the spin–orbit coupling can be neglected in the study of these properties. Finally, we compared the wavenumber and atomic displacement patterns of corresponding Raman-active modes in tilkerodeite and jacutingaite, and found that the effect of the Pd and Pt masses can be neglected on reasoning their wavenumber differences. From this analysis, tilkerodeite is found to be mechanically weaker than jacutingaite against the atomic displacement patterns of these modes. Our findings advance the understanding of the structural properties of a recently discovered layered topological insulator, fundamental to further exploring its electronic, optical, thermal, and mechanical properties, and for device fabrication.