# Two-dimensional conical dispersion in ZrTe5 evidenced by optical spectroscopy

## TL;DR

This study uses optical and transport measurements to show that ZrTe5 exhibits a two-dimensional conical dispersion in the a-c plane, challenging the previous 3D Dirac semimetal model and revealing anisotropic electronic behavior.

## Contribution

It provides new experimental evidence that ZrTe5's electronic dispersion is anisotropic, with linear behavior only in two dimensions, contradicting the 3D Dirac semimetal hypothesis.

## Key findings

- Dispersion is linear in the a-c plane only
- Remaining flat and parabolic along the b axis
- ZrTe5 cannot be modeled as a 3D Dirac semimetal

## Abstract

Zirconium pentatelluride was recently reported to be a 3D Dirac semimetal, with a single conical band, located at the center of the Brillouin zone. The cone's lack of protection by the lattice symmetry immediately sparked vast discussions about the size and topological/trivial nature of a possible gap opening. Here we report on a combined optical and transport study of ZrTe5, which reveals an alternative view of electronic bands in this material. We conclude that the dispersion is approximately linear only in the a-c plane, while remaining relatively flat and parabolic in the third direction (along the b axis). Therefore, the electronic states in ZrTe5 cannot be described using the model of 3D Dirac massless electrons, even when staying at energies well above the band gap 6 meV found in our experiments at low temperatures.