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.

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• Electronic structure
• Topological materials
• Two-dimensional electron system
• Angle-resolved photoemission spectroscopy
• Scanning tunneling microscopy