Blue phosphorene bilayer is a two-dimensional metal -- and an unambiguous classification scheme for buckled hexagonal bilayers

TL;DR

First-principles calculations reveal blue phosphorene bilayer as a stable two-dimensional metal with a novel stacking configuration, providing a new classification scheme for buckled hexagonal bilayers and potential for phosphorus-based transistors.

Contribution

Introduces a comprehensive classification scheme for buckled honeycomb bilayers and identifies a previously unreported stable metallic stacking configuration of blue phosphorene bilayer.

Findings

Blue phosphorene bilayer is a stable 2D metal.

Most stable stacking configuration is metallic.

All stacking configurations are experimentally accessible.

Abstract

High-level first-principles computations predict blue phosphorene bilayer to be a two-dimensional metal. This structure has not been considered before and was identified by employing a block-diagram scheme that yields the complete set of five high-symmetry stacking configurations of buckled honeycomb layers, and allows their unambiguous classification. We show that all of these stacking configurations are stable or at least metastable configurations both for blue phosphorene and gray arsenene bilayers. For blue phosphorene, the most stable stacking configuration has not yet been reported, and surprisingly it is metallic, while all other arrangements are indirect band gap semiconductors. As it is impossible to interchange the stacking configurations by translations, all of them should be experimentally accessible via the transfer of monolayers. The metallic character of blue phosphorene bilayer is caused by its short interlayer distance of 3.01 {\AA} and offers the exceptional possibility to design single elemental all-phosphorus transistors.