The Microscopic Diamond Anvil Cell: Stabilization of Superhard, Superconducting Carbon Allotropes at Ambient Pressure

TL;DR

This paper predicts a new metastable carbon allotrope with superhardness and superconductivity at ambient pressure, stabilized by a microscopic diamond anvil cell structure, and suggests its potential synthesis via cold compression of graphite.

Contribution

It introduces a novel carbon phase combining superhardness and superconductivity, stabilized by an intrinsic microscopic diamond anvil cell structure, and explores its tunable properties.

Findings

Predicted a metallic, superconducting carbon allotrope with sp3 and sp2 bonding.

Estimated Vickers hardness of 48 GPa for the phase.

Proposed synthesis via cold compression of graphite at 40 GPa.

Abstract

A metallic covalently bonded carbon allotrope is predicted via first principles calculations. It is composed of an $sp^3$ carbon framework that acts as a diamond anvil cell by constraining the distance between parallel cis-polyacetylene chains. The distance between these $sp^2$ carbon atoms renders the phase metallic, and yields two well-nested nearly parallel bands that span the Fermi level. Calculations show that this phase is a conventional superconductor, with the motions of the $sp^2$ carbons being key contributors to the electron phonon coupling. The $sp^3$ carbon atoms impart superior mechanical properties, with a predicted Vickers hardness of 48~GPa. This phase, metastable at ambient conditions, could be made via cold compression of graphite to 40~GPa. A family of multifunctional materials with tunable superconducting and mechanical properties could be derived from this phase by varying the $sp^2$ versus $sp^3$ carbon content and by doping.