Electron-phonon interaction in In-induced structures on Si(111) from first-principles.

Electron-phonon interaction in the Si(111)-supported rectangular phases of In is investigated within the density-functional theory and linear-response. For both single-layer and double-layer structures, it is found that the phonon-induced scattering of electrons is almost exclusively determined by vibrations of In atoms. It is shown that the strength of electron-phonon coupling at the Fermi level λ(EF) increases almost twofold upon adding the second In layer. One of the reasons is that additional low-frequency modes appear in the phonon spectrum, which favors a strong enhancement of λ(EF). The agreement of the calculated parameter λ(EF) = 0.99 for a double-layer structure as well as the superconducting transition temperature Tc = 3.5 K with experimental estimates indicates that the discovered superconducting phase is probably a double-layer rectangular -In structure on Si(111) with a coverage of 2.4 ML. This conclusion is also supported by good agreement between the calculated electron band structure and ARPES measurements.

Electron-phonon coupling in topological surface states: The role of polar optical modes.

The use of topological edge states for spintronic applications could be severely hampered by limited lifetimes due to intrinsic many-body interactions, in particular electron-phonon coupling. Previous works to determine the intrinsic coupling strength did not provide a coherent answer. Here, the electron-phonon interaction in the metallic surface state of 3D topological insulators is revised within a first principles framework. For the archetypical cases of Bi2Se3 and Bi2Te3, we find an overall weak coupling constant of less than 0.15, but with a characteristic energy dependence. Derived electronic self-energies compare favorably with previous angle-resolved photoemission spectroscopy results. The prevailing coupling is carried by optical modes of polar character, which is weakly screened by the metallic surface state and can be reduced by doping into bulk bands. We do not find any indication of a strong coupling to the A1g mode or the presence of a Kohn anomaly in the surface phonon spectrum. The weak intrinsic electron-phonon coupling guarantees long-lived quasiparticles at elevated temperatures.

Raman Spectroscopy of Lattice-Matched Graphene on Strongly Interacting Metal Surfaces.

Regardless of the widely accepted opinion that there is no Raman signal from single-layer graphene when it is strongly bonded to a metal surface, we present Raman spectra of a graphene monolayer on Ni(111) and Co(0001) substrates. The high binding energy of carbon to these surfaces allows formation of lattice-matched (1 × 1) structures where graphene is significantly stretched. This is reflected in a record-breaking shift of the Raman G band by more than 100 cm-1 relative to the case of freestanding graphene. Using electron diffraction and photoemission spectroscopy, we explore the aforementioned systems together with polycrystalline graphene on Co and analyze possible intercalation of oxygen at ambient conditions. The results obtained are fully supported by Raman spectroscopy. Performing a theoretical investigation of the phonon dispersions of freestanding graphene and stretched graphene on the strongly interacting Co surface, we explain the main features of the Raman spectra. Our results create a reliable platform for application of Raman spectroscopy in diagnostics of chemisorbed graphene and related materials.