Electronic structure and electron-phonon coupling in the 18 K superconductor Y_2C_3

摘要

The electronic structure and electron-phonon coupling in Y_2C_3 is investigated using density functional calculations. We find that the Fermi level falls in a manifold of mixed character derived from Y d states and antibonding states associated with the C dimers in the structure. Calculations of the electron-phonon coupling for Y and C modes show that the former provide most of the coupling. Modes associated with C-C bond stretching have large matrix elements, but make small contributions to the coupling because of their high phonon frequencies. Substantial electron doping of the C-C antibonding states would yield a large increase in the coupling and critical temperature, perhaps to values comparable to MgB_2. However, it seems unlikely that a modification of Y_2C_3 with much higher filling of the C-C antibonding states can be stabilized.