Experimental Observation of Three-Component 'New Fermions' in Topological Semimetal MoP

TL;DR

This study reports the experimental discovery of triply degenerate fermions in the topological semimetal MoP, revealing novel quasiparticles beyond traditional classifications and their coexistence with Weyl points.

Contribution

First experimental observation of three-component 'new fermions' in MoP, expanding the understanding of quasiparticles in topological materials.

Findings

Identification of triply degenerate points in MoP

Coexistence of new fermions with Weyl points

Use of angle-resolved photoemission spectroscopy

Abstract

Condensed matter systems can host quasiparticle excitations that are analogues to elementary particles such as Majorana, Weyl, and Dirac fermions. Recent advances in band theory have expanded the classification of fermions in crystals, and revealed crystal symmetry-protected electron excitations that have no high-energy counterparts. Here, using angle-resolved photoemission spectroscopy, we demonstrate the existence of a triply degenerate point in the electronic structure of MoP crystal, where the quasiparticle excitations are beyond the Majorana-Weyl-Dirac classification. Furthermore, we observe pairs of Weyl points in the bulk electronic structure coexisting with the 'new fermions', thus introducing a platform for studying the interplay between different types of fermions.