Structural Stability and Anisotropic Electron-Phonon Interactions in Excitonic Insulator Candidate Ta₂Pd₃Te₅

Excitonic insulator (EI) is a macroscopic quantum coherent state that arises from the spontaneous condensation of excitons—electron-hole pairs—in narrow-gap semiconductors or semimetals. This condensation is driven by the attractive Coulomb interaction, and leads to the opening of a many-body gap in the electronic structure. Despite the profound theoretical interest, experimental realization and unambiguous identification of EI in real materials have been remarkably challenging. The primary obstacle is the difficulty of disentangling the excitonic instability from other competing or coexisting instabilities, particularly structural instabilities. We investigate Ta₂Pd₃Te₅, a proposed EI candidate, using temperature-dependent and angle-resolved polarized Raman spectroscopy. No splitting of existing phonon modes or emergence of new modes are observed across the predicted transition temperatures, confirming the structural stability and excluding lattice distortions. The A_g phonon modes reveal strong anisotropic electron–phonon interactions (EPIs), further supported by density-functional perturbation calculations. The clear presence of such coupling suggests that anisotropic EPIs, when incorporated into quantum many-body models, may need to be considered in the excitonic gap formation. These results identify Ta₂Pd₃Te₅ as a robust platform for exploring the interplay between excitonic correlations and electron–phonon interactions in low-dimensional quantum materials.