Strong Quantized Electron–Phonon Coupling Induced by the Unique LA Phonon Mode in 2D Kramers Semimetal InTe

Two-dimensional topological materials with flat bands and van Hove singularities in their electronic band structures are common, and these features may lead to superconductivity due to the strong condensation of electronic states. However, the electron–phonon coupling between flat bands and single longitudinal acoustic (LA) phonons has not been extensively studied or reported. In this work, using group theory, symmetry analysis, and first-principles calculations, we investigate flat electron bands, phonon spectra, and electron–phonon coupling in a two-dimensional metallic InTe monolayer. Our study reveals that the electron–phonon interaction in the intrinsic Kramers nodal line, with a van Hove singularity near the Fermi level, primarily involves a single LA phonon mode that couples strongly with the flat band electrons. This interaction leads to a slightly anisotropic superconducting gap function. Our findings provide new insights into the role of phonon-mediated electron interactions in superconductors with flat bands.