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.

• Received 15 December 2020
• Revised 12 August 2021
• Accepted 6 December 2021

DOI:https://doi.org/10.1103/PhysRevB.104.L241408