Eightfold Fermionic Excitation in a Charge Density Wave Compound

TL;DR

This paper reports the discovery of eightfold fermionic excitations in the charge density wave compound TaTe4, demonstrating that charge density waves can induce new topological phases with unconventional quasiparticles.

Contribution

It provides experimental evidence of eightfold fermionic excitations in TaTe4, a charge density wave material, linking charge density waves to novel topological quasiparticles.

Findings

Identification of eightfold fermionic excitations in TaTe4

Observation of a pseudogap of about 45 meV on the surface

Detection of atomic step edge states via STM

Abstract

Unconventional quasiparticle excitations in condensed matter systems have become one of the most important research frontiers. Beyond two- and fourfold degenerate Weyl and Dirac fermions, three-, six- and eightfold symmetry protected degeneracies have been predicted however remain challenging to realize in solid state materials. Here, charge density wave compound TaTe4 is proposed to hold eightfold fermionic excitation and Dirac point in energy bands. High quality TaTe4 single crystals are prepared, where the charge density wave is revealed by directly imaging the atomic structure and a pseudogap of about 45 meV on the surface. Shubnikov de-Haas oscillations of TaTe4 are consistent with band structure calculation. Scanning tunneling microscopy reveals atomic step edge states on the surface of TaTe4. This work uncovers that charge density wave is able to induce new topological phases and sheds new light on the novel excitations in condensed matter materials.