Two-gap superconductivity in heavily n-doped graphene: ab initio Migdal-Eliashberg theory

TL;DR

This study uses first-principles Migdal-Eliashberg theory to predict possible superconductivity in heavily doped graphene, revealing a two-gap structure in n-doped cases and suggesting experimental feasibility at high carrier densities.

Contribution

It provides the first ab initio prediction of two-gap superconductivity in heavily n-doped graphene using anisotropic Migdal-Eliashberg calculations.

Findings

Superconducting gaps with s-wave symmetry are predicted.

A two-gap structure similar to MgB2 is found in n-doped graphene.

Superconductivity may be observable at carrier densities above 10^15 cm^-2.

Abstract

Graphene is the only member of the carbon family from zero- to three-dimensional materials for which superconductivity has not been observed yet. At this time, it is not clear whether the quest for superconducting graphene is hindered by technical challenges, or else by the fluctuation of the order parameter in two dimensions. In this area, ab initio calculations are useful to guide experimental efforts by narrowing down the search space. In this spirit, we investigate from first principles the possibility of inducing superconductivity in doped graphene using the fully anisotropic Migdal-Eliashberg theory powered by Wannier-Fourier interpolation. To address a best-case scenario, we consider both electron and hole doping at high carrier densities, so as to align the Fermi level to a van Hove singularity. In these conditions, we find superconducting gaps of $s$-wave symmetry, with a slight anisotropy induced by the trigonal warping, and, in the case of $n$-doped graphene, an unexpected two-gap structure reminiscent of MgB$_2$. Our Migdal-Eliashberg calculations suggest that the observation of superconductivity at low temperature should be possible for $n$-doped graphene at carrier densities exceeding $10^{15}$ cm$^{-2}$.