Unconventional superconductivity in YPtBi and related topological semimetals

TL;DR

This paper investigates the unconventional superconductivity in YPtBi, a topological semimetal with low carrier density, suggesting that traditional electron-phonon coupling cannot explain its superconducting properties, implying an alternative pairing mechanism.

Contribution

The study provides evidence that unconventional pairing mechanisms are likely responsible for superconductivity in YPtBi, challenging the conventional electron-phonon theory.

Findings

Conventional electron-phonon coupling cannot account for observed T_c at low carrier densities.

Relativistic density functional theory shows high carrier concentration needed for conventional pairing.

Unconventional pairing mechanisms are likely responsible for superconductivity in YPtBi.

Abstract

YPtBi, a topological semimetal with very low carrier density, was recently found to be superconducting below $T_\mathrm{c} = 0.77$\,K. In the conventional theory, the nearly vanishing density of states around the Fermi level would imply a vanishing electron-phonon coupling and would therefore not allow for superconductivity. Based on relativistic density functional theory calculations of the electron-phonon coupling in YPtBi it is found that carrier concentrations of more than $10^{21}$\,cm$^{-3}$ are required to explain the observed critical temperature with the conventional pairing mechanism, which is several orders of magnitude larger than experimentally observed. It is very likely that an unconventional pairing mechanism is responsible for the superconductivity in YPtBi and related topological semimetals with the Half-Heusler structure.