Direct observation of six-fold exotic fermions in topological semimetal PdSb$_2$

TL;DR

This study provides direct spectroscopic evidence of six-fold exotic fermions in the topological semimetal PdSb$_2$, confirming theoretical predictions and revealing unique band structures with potential for novel topological applications.

Contribution

First direct observation of six-fold fermions in PdSb$_2$ using ARPES, validating theoretical models and expanding understanding of topological fermions in nonsymmorphic materials.

Findings

Verification of six-fold fermions at the R point in PdSb$_2$

Bands exhibit parabolic dispersion near six-fold fermion nodes

No protected Fermi arcs observed, consistent with achiral structure

Abstract

Pyrite-type PdSb$_2$ with a nonsymmorphic cubic structure has been predicted to host six-fold-degenerate exotic fermions beyond the Dirac and Weyl fermions. Though magnetotransport measurements on PdSb$_2$ suggest its topologically nontrivial character, direct spectroscpic study of its band structure remains absent. Here, by utilizing high-resolution angle-resolved photoemission spectroscopy, we present a systematic study on its bulk and surface electronic structure. Through careful comparison with first-principles calculations, we verify the existence of six-fold fermions in PdSb$_2$, which are formed by three doubly degenerate bands centered at the $R$ point in the Brillouin zone. These bands exhibit parabolic dispersion close to six-fold fermion nodes, in sharp contrast to previously reported ones in chiral fermion materials. Furthermore, our data reveal no protected Fermi arcs in PdSb$_2$, which is compatible with its achiral structure. Our findings provide a remarkable platform for study of new topological fermions and indicate their potential applications.