Electronic Structure and Electron-Phonon Coupling in the 18K Superconductor Y2C3

TL;DR

This study uses density functional calculations to analyze the electronic structure and electron-phonon interactions in Y2C3, revealing key modes contributing to superconductivity and potential ways to enhance the critical temperature.

Contribution

It provides new insights into the electron-phonon coupling mechanisms in Y2C3 and suggests doping strategies to potentially increase its superconducting temperature.

Findings

Y2C3's Fermi level is in a mixed character manifold of Y d states and C dimer antibonding states.

Y modes dominate the electron-phonon coupling, while C-C bond stretching modes have high frequencies and small contributions.

Electron doping of C-C antibonding states could significantly increase the coupling and T_c, but stabilization is unlikely.

Abstract

The electronic structure and electron-phonon coupling in Y2C3 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 MgB2. However, it seems unlikely that a modification of Y2C3 with much higher filling of the C-C antibonding states can be stabilized.