Strong electron-phonon coupling in the rare-earth carbide superconductor La2C3

TL;DR

This study investigates the strong electron-phonon coupling in La2C3, revealing its role in superconductivity with a coupling constant of about 1.35, and highlights the importance of La-related phonon modes.

Contribution

It provides a detailed analysis combining neutron diffraction, specific heat, and electronic structure calculations to quantify electron-phonon coupling in La2C3, emphasizing its strong coupling nature.

Findings

Electron-phonon coupling constant a a 1.35

Superconductivity primarily driven by La-related phonon modes

Enhanced upper critical field beyond WHH prediction

Abstract

We present the results of a crystal structure determination using neutron powder diffraction as well as the superconducting properties of the rare-earth sesquicarbide La2C3 (Tc ~ 13.4 K) by means of specific heat and upper critical field measurements. From the detailed analysis of the specific heat and a comparison with ab-initio electronic structure calculations, a quantitative estimate of the electron-phonon coupling strength and the logarithmic average phonon frequency is made. The electron-phonon coupling constant is determined to \lambda ~ 1.35. The electron-phonon coupling to low energy phonon modes is found to be the leading mechanism for the superconductivity. Our results suggest that La2C3 is in the strong coupling regime, and the relevant phonon modes are La-related rather than C-C stretching modes. The upper critical field shows a clear enhancement with respect to the Werthamer-Helfand-Hohenberg prediction, consistent with strong electron-phonon coupling. Possible effects on the superconducting properties due to the noncentrosymmetry of the crystal structure are discussed.