Electron Phonon Interactions in C28-derived Solids
- Powerpoint version
Objectives:
Reliable computational methods to predict new solids with desired mechanical properties, metallic character, and enhanced electron-phonon coupling for superconductivity.
Approach:
Simulations using the pseudopotential density functional SIESTA code, coupled with tight-binding and other codes.
Previous work:
We have shown that solids can be formed from C28-derived molecules and predicted the properties of doped systems. Solid C28H4 is found to bind weakly and exhibits many of the electronic structure features of solid C60. Chemical doping is feasible, and we predict that the increased electron-phonon coupling leads to superconducting transition temperatures exceeding those of the alkali-doped C60 solids. (N. A. Romero, J. Kim and R.M Martin, Phys. Rev. B, 70 140504, 2004.)
New Results:
We have shown that strongly bound solids formed from the reactive C28 molecule can be doped and the states near the Fermi energy acts very much as in molecular solids. This opens the possibility of molecular-like doping and superconductivity in a strong covalently bonded solid. Chemical doping is feasible, and electron phonon interactions are large. However, structures investigated so far show distortions that reduce the metallic conductivity.
Larger context:
New routes to materials with mechanical strength of diamond, dopable to be good metals, and superconductors with high transition temperatures. Development of codes for computational materials science. Training of students in basic science and applications.
Comparison of the band structure and density of states (DOS in states/eV/spin/cell) of strongly-bonded solid C28 in the "hyperwurtzite"structure. The left figure shows the wide band gap of the insulating solid. , and the right figure shows the metallic bands by endohedral doping of Zr. The bands are very molecular-like with large density of states and large electon-phonon coupling much like C60 molecular solids.
