We report an experimental and theoretical study of the electron-phonon coupling for $\alpha \text{−}\mathrm{Sn}/\mathrm{Ge}\left(111\right)$, a prototypical triangular lattice surface, closely related to $\mathrm{Sn}/\mathrm{Si}\left(111\right)\text{−}(\sqrt{3}\times \sqrt{3})$, where recent experimental evidence has found superconductivity [X. Wu et al., Phys. Rev. Lett. 125, 117001 (2020)]. We concentrate our study on the ($3\times 3$) phase of $\alpha \text{−}\mathrm{Sn}/\mathrm{Ge}\left(111\right)$ that appears between 150 and 120 K and has a well-known geometry with a half-filled electronic band around the Fermi energy. We show that this surface presents a giant electron-phonon interaction that can be considered at least partially responsible for the different phases that this system shows at very low temperature. Our theoretical results indicate that indeed the electron-phonon interaction in $\alpha \text{−}\mathrm{Sn}/\mathrm{Ge}\left(111\right)\text{−}(3\times 3)$ is unusually large, since we find that $\lambda$, the electron mass enhancement for the half-filled band, is $\lambda =1.3$. This result is in good agreement with the experimental value obtained from high-resolution angle-resolved photoemission spectroscopy measurements, which yield $\lambda =1.45\pm 0.1$.

• Received 1 April 2022
• Revised 30 November 2022
• Accepted 13 December 2022

DOI:https://doi.org/10.1103/PhysRevB.107.045303