Using ab-initio density functional theory for superconductors (SCDFT), we systematically study the quaternary borocarbides RM2B2C. Treating the retarded (frequency-dependent) interaction W(ω) within the random-phase approximation (RPA), we find good agreement with experiments for the calculated superconducting critical temperature Tc in the nonmagnetic Ni- and Pd-based compounds. We argue that the problem of accurately placing the f-bands within DFT, and possibly the lack of an explicit magnetic pair-breaking mechanism, explain the difficulties of SCDFT in reproducing Tc in members of the magnetic RNi2B2C series (R rare-earth with partially filled 4f). While the calculated Tc is overestimated, SCDFT qualitatively captures the experimentally observed trend along the rare-earth series, which indicates that the electron-phonon couplings and dynamically screened interactions have a significant effect on Tc.
@article{arxiv.2310.03723,
title = {Quaternary borocarbides: a testbed for DFT for superconductors},
author = {Viktor Christiansson and Philipp Werner},
journal= {arXiv preprint arXiv:2310.03723},
year = {2026}
}