High-Pressure Synthesis of a Massive and Non-Symmorphic Dirac Semimetal Candidate MoP$_4$

TL;DR

This study reports the high-pressure synthesis of MoP$_4$, a layered Zintl compound with non-symmorphic symmetry, exhibiting Dirac nodes and semi-metallic properties, highlighting its potential as a topological semimetal candidate.

Contribution

It introduces a high-pressure synthesis method for MoP$_4$ and demonstrates its Dirac semimetal features due to non-symmorphic symmetry and spin-orbit coupling effects.

Findings

MoP$_4$ exhibits large positive magnetoresistance and high-mobility electrons.

Band structure reveals Dirac nodes slightly below the Fermi level.

Non-symmorphic symmetry protects certain Dirac crossings from spin-orbit coupling effects.

Abstract

Single crystal and polycrystalline samples of MoP$_4$ with a black-phosphorus-derived structure have been successfully synthesized by a high-pressure technique. The polycrystalline samples show a large positive magnetoresistance and a small negative Seebeck coefficient at low temperatures, reflecting a semi-metallic nature with high-mobility electrons. Consistent with the transport properties, the band structure calculation reveals a semi-metallic state with the presence of two types of Dirac nodes slightly below the Fermi level. The Dirac node along the $\Gamma$-X direction normal to the phosphorus layers is gapped out in the presence of spin-orbit coupling (SOC), whereas the band crossing at the Z-point is immune to SOC because of the non-symmorphic symmetry. This work demonstrates a great potential of phosphorus-based layered Zintl compounds for topological semimetal candidates allowing chemical band engineering.