Raman-scattering study of the electron-phonon interaction in M3C60 (M=K,Rb)

Evidence of strong and mode-selective electron-phonon coupling in the topological superconductor candidate 2M-WS2

The interaction between lattice vibrations and electrons plays a key role in various aspects of condensed matter physics - including electron hydrodynamics, strange metal behavior, and high-temperature superconductivity. In this study, we present systematic investigations using Raman scattering and angle-resolved photoemission spectroscopy (ARPES) to examine the phononic and electronic subsystems of the topological superconductor candidate 2M-WS2. Raman scattering exhibits an anomalous nonmonotonic temperature dependence of phonon linewidths, indicative of strong phonon-electron scattering over phonon-phonon scattering. The ARPES results demonstrate pronounced dispersion anomalies (kinks) at multiple binding energies within both bulk and topological surface states, indicating a robust and mode-selective coupling between the electronic states and various phonon modes. These experimental findings align with previous calculations of the Eliashberg function, providing a deeper understanding of the highest superconducting transition temperature observed in 2M-WS2 (8.8 K) among all transition metal dichalcogenides as induced by electron-phonon coupling. Furthermore, our results may offer valuable insights into other properties of 2M-WS2 and guide the search for high-temperature topological superconductors.

Evidence for Band Renormalizations in Strong-Coupling Superconducting Alkali-Fulleride Films

There has been a long-standing debate about the mechanism of the unusual superconductivity in alkali-intercalated fullerides. In this Letter, using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the electronic structures of superconducting K_{3}C_{60} thin films. We observe a dispersive energy band crossing the Fermi level with the occupied bandwidth of about 130 meV. The measured band structure shows prominent quasiparticle kinks and a replica band involving the Jahn-Teller active phonon modes, which reflects strong electron-phonon coupling in the system. The electron-phonon coupling constant is estimated to be about 1.2, which dominates the quasiparticle mass renormalization. Moreover, we observe an isotropic nodeless superconducting gap beyond the mean-field estimation (2Δ/k_{B}T_{c}≈5). Both the large electron-phonon coupling constant and large reduced superconducting gap suggest a strong-coupling superconductivity in K_{3}C_{60}, while the electronic correlation effect is suggested by the observation of a waterfall-like band dispersion and the small bandwidth compared with the effective Coulomb interaction. Our results not only directly visualize the crucial band structure but also provide important insights into the mechanism of the unusual superconductivity of fulleride compounds.

Quantifying vibronic coupling with resonant inelastic X-ray scattering

Electron–phonon interactions are fundamental to the behavior of chemical and physical systems.

Raman Spectroscopy of Two-Dimensional Borophene Sheets

The successful fabrication of a two-dimensional boron sheet, which features a triangular lattice with periodic hole arrays, has stimulated great interest in its specific structure as well as properties such as possible superconductivity. Here, we report a study on the vibrational spectra and electron-phonon coupling (EPC) in monolayer boron sheets by in situ Raman and tip-enhanced Raman spectroscopy (TERS) at low temperature and ultrahigh vacuum. The gap-mode TERS gives a 3 × 10⁹ selective enhancement on vertical vibrational Raman modes. A spatial resolution of 1 nm is achieved in this system. Combined with first-principle calculations, the vibrational properties as well as EPC in borophene are determined. The results are helpful for further study on the mechanical, electronic, and possible superconducting properties of two-dimensional boron.

Raman study of the electron-phonon interaction in light alkali metal intercalated metallic fullerides

By laser-irradiating polymeric Li(4)C(60) and Na(4)C(60), we have obtained pure monomeric metallic phases stable at ambient conditions. Based on a systemic Raman analysis, we have determined the electron-phonon coupling constant for both metallic phases. The e-p coupling constants of Li- and Na-intercalated metallic fullerides are smaller than those of superconductive K(3)C(60) and Rb(3)C(60) and comparable to or slightly higher than that of ambient-pressure non-superconductive Cs(3)C(60). We predict that Na-doped fulleride could exhibit superconductivity with T(c) ∼ 10 K. Much lower T(c) or even no superconductivity can be expected for the Li-doped fulleride which exhibits a strong Li(+)-C interaction. These results contribute to the understanding of superconductivity in light alkali metal intercalated fullerides.