Observation of topological edge states in the quantum spin Hall insulator Ta2Pd3Te5

Two-dimensional topological insulators (2DTIs), which host the quantum spin Hall (QSH) effect, are one of the key materials in next-generation spintronic devices. To date, experimental evidence of the QSH effect has only been observed in a few materials, and thus, the search for new 2DTIs is at the forefront of physical and materials science. Here, we report experimental evidence of a 2DTI in the van der Waals material ${\mathrm{Ta}}_{2}{\mathrm{Pd}}_{3}{\mathrm{Te}}_{5}$. First-principles calculations show that each monolayer of ${\mathrm{Ta}}_{2}{\mathrm{Pd}}_{3}{\mathrm{Te}}_{5}$ is a 2DTI with weak interlayer interactions. Combined transport, angle-resolved photoemission spectroscopy, and scanning tunneling microscopy measurements confirm the existence of a band gap at the Fermi level and topological edge states inside the gap. These results demonstrate that ${\mathrm{Ta}}_{2}{\mathrm{Pd}}_{3}{\mathrm{Te}}_{5}$ is a promising material for fabricating spintronic devices based on the QSH effect.