Spin fluctuations, electron-phonon coupling and superconductivity in near-magnetic elementary metals; Fe,Co,Ni and Pd

TL;DR

This paper explores the potential for superconductivity mediated by spin fluctuations in elementary metals like Fe, Co, Ni, and Pd, emphasizing the role of magnetic instabilities and electron-phonon interactions.

Contribution

It provides detailed calculations of electron-phonon and spin-fluctuation couplings in various phases of these metals, highlighting conditions favorable for superconductivity.

Findings

Superconductivity is most likely near magnetic instabilities.

Fcc Ni's stable magnetism makes it less interesting for spin-fluctuation mediated superconductivity.

High-pressure fcc Co shows potential for measurable T$_C$ based on spin fluctuations.

Abstract

An investigation of possibilities for superconductivity mediated by spin fluctuations in some elementary metals is motivated by the recent discovery of superconductivity in the hcp high-pressure phase of iron. The electronic structure, the electron-phonon coupling ($\lambda_{ph}$) and the coupling due to spin-fluctuations ($\lambda_{sf}$) are calculated for different phases and different volumes for four elementary metals. The results show that such possibilities are best for systems near, but on the non-magnetic side of, a magnetic instability. Fcc Ni, which show stable magnetism over a wide pressure range, is not interesting in this respect. Ferro- and antiferro-magnetic fluctuations in hcp Fe contribute to a relatively strong coupling in the pressure range where superconductivity is observed. The absence of fluctuations at large q-vectors makes fcc Pd only moderately interesting despite its large exchange enhancement for q=0. Fcc Co at high pressure ($\sim$ 0.5 Mbar) behaves as an improved version of Pd, where the fluctuations extend to larger q. The estimations of T$_C$, which reproduce the experimental situation in Fe quite well, suggest a measurable T$_C$ for the high-pressure phase of fcc Co, while the estimate is lower for the ambient-pressure phase of fcc Pd.