Charge order induced Dirac pockets in the nonsymmorphic crystal TaTe$_4$

TL;DR

This study reveals how charge order in the nonsymmorphic crystal TaTe$_4$ induces Dirac and double Dirac fermions, highlighting the interplay between charge order and topological band features through experimental and computational evidence.

Contribution

It demonstrates that charge order in TaTe$_4$ leads to the emergence of Dirac fermions and double Dirac fermions, expanding understanding of topological states induced by charge ordering.

Findings

Charge order induces Dirac fermion-related bands near the Fermi level.

Band folding aligns with the new periodicity from charge order.

Evidence of double Dirac fermions in the system.

Abstract

The interplay between charge order (CO) and nontrivial band topology has spurred tremendous interest in understanding topological excitations beyond the single-particle description. In a quasi-one-dimensional nonsymmorphic crystal TaTe$_4$, the (2a$\times$2b$\times$3c) charge ordered ground state drives the system into a space group where the symmetry indicator features the emergence of Dirac fermions and unconventional double Dirac fermions. Using angle-resolved photoemission spectroscopy and first-principles calculations, we provide evidence of the CO induced Dirac fermion-related bands near the Fermi level. Furthermore, the band folding at the Fermi level is compatible with the new periodicity dictated by the CO, indicating that the electrons near the Fermi level follow the crystalline symmetries needed to host double Dirac fermions in this system.