Electron-Phonon Interactions in C$_{28}$-derived Molecular Solids

Electron-phonon interaction in the solid form of the smallest fullerene C$_{20}$

The electron-phonon coupling of a theoretically devised carbon phase made by assembling the smallest fullerenes C$_{20}$ is calculated from first principles. The structure consists of C$_{20}$ cages in an {\it fcc} lattice interlinked by two bridging carbon atoms in the interstitial tetrahedral sites ({\it fcc}-C$_{22}$). The crystal is insulating but can be made metallic by doping with interstitial alkali atoms. In the compound NaC$_{22}$ the calculated coupling constant $λ/N(0)$ is 0.28 eV, a value much larger than in C$_{60}$, as expected from the larger curvature of C$_{20}$. On the basis …

Experimental Determination of Electron Transition Probabilities in Elementary Electron-Phonon Scattering Processes Using Electron-Energy-Loss Spectroscopy: The Example of Graphite

We have investigated coupling constants in elementary electron-phonon scattering processes on a graphite surface by the combined use of high-resolution electron-energy-loss spectroscopy (HREELS) and very low-energy electron diffraction (VLEED). HREELS is used to measure the modulations of electron transition probabilities from incoming electrons in vacuum to outgoing electrons in vacuum where the transition includes one-phonon scattering processes inside a solid. Determining the electronic band structures of graphite with VLEED, we defined electronic states of the solid surface that electrons …

Phonon deficit effect and solid state refrigerators based on superconducting tunnel junctions

Thin film devices have the advantage of being extremely compact, operate in a continuous mode, dissipate little power, and can easily be integrated in cryogenic detectors. Motivated by such possibilities, we investigate the phonon deficit effect in thin film $SIS$ (superconductor--insulator--superconductor) and $SIN$ tunnel junctions. Under certain circumstances, the phonon absorption spectra of such tunnel junctions have spectral windows of phonon absorption/emission. We propose to use phonon filters to select the phonon absorbtion windows and thus to enhance the cooling effect. Membranes att…

声子线型对固态氢超导性的巨大影响

Large impact of phonon lineshapes on the superconductivity of solid hydrogen

本研究探讨了非洛伦兹声子线型对高压固态氢超导性的影响，通过从头计算完整声子谱函数发现声子软化与线展宽对超导临界温度T_C分别产生增强和降低作用，总体提升了T_C估计值，并揭示了450-500 GPa下氢分子相VI的超导性，解释了理论与实验的分歧。

Vibrational spectrum and electron-phonon coupling of doped solid picene from first principles

We study superconductivity in doped solid picene (C22H14) with linear response calculations of the phonon spectrum and electron-phonon (ep) interaction. We show that the coupling of the high-energy C bond-stretching phonons to the π molecular orbitals for a doping of ~3 electrons per picene molecule is sufficiently strong to reproduce the experimental Tc of 18 K within Migdal-Eliashberg theory. For hole doping, we predict a similar coupling leading to a maximum Tc of 6 K. However, we argue that, due to its molecular nature, picene may belong to the same class of strongly correlated ep supercon…

Electron-Phonon Interaction and Raman Linewidth in Superconducting Fullerides

We propose a microscopic theory of interaction of long wave molecular phonons with electrons in fullerides in the presence of disorder. Phonon relaxation rate and frequency renormalization are discussed. Finite electronic bandwidth reduces phonon relaxation rate at $q=0$. Electron-phonon coupling constants with molecular modes in fullerides are estimated. The results are in good agreement with photoemission experiments.