The Next Breakthrough in Phonon-Mediated Superconductivity

TL;DR

This paper reviews recent high-temperature superconductors like MgB2 and high-pressure Li, aiming to understand their unexpected properties and explore future possibilities in phonon-mediated superconductivity.

Contribution

It provides a simplified understanding of recent UHTS materials and discusses potential future directions in phonon-coupled superconductivity.

Findings

MgB2 has Tc=40 K, high-pressure Li has Tc=20 K

Layered structures and strong C-C or B-C bonds are common in UHTS

Unresolved puzzles remain in the understanding of these materials

Abstract

If history teaches us anything, it is that the next breakthrough in superconductivity will not be the result of surveying the history of past breakthroughs, as they have almost always been a matter of serendipity resulting from undirected exploration into new materials. Still, there is reason to reflect on recent advances, work toward higher T_c of even an incremental nature, and recognize that it is important to explore avenues currently believed to be unpromising even as we attempt to be rational. In this paper we look at two remarkable new unusually high temperature superconductors (UHTS), MgB2 with Tc=40 K and (in less detail) high pressure Li with Tc=20 K, with the aim of reducing their unexpected achievements to a simple and clear understanding. We also consider briefly other UHTS systems that provide still unresolved puzzles; these materials include mostly layered structures, and several with strongly bonded C-C or B-C substructures. What may be possible in phonon-coupled superconductivity is reconsidered in the light of the discussion.