# Metal-chalcogen bond-length induced electronic phase transition from semiconductor to topological semimetal in ZrX$_2$ (X = Se and Te)

## TL;DR

This study combines ARPES and DFT to reveal that ZrTe₂ is a topological semimetal with a band inversion, and demonstrates how changing metal-chalcogen bond lengths induces a transition from semiconductor to semimetal.

## Contribution

It provides the first experimental and theoretical evidence that ZrTe₂ is a topological semimetal and links the electronic phase transition to metal-chalcogen bond length variations.

## Key findings

- ZrTe₂ exhibits free charge carriers at the Fermi level.
- Band inversion between Te p and Zr d states indicates non-trivial topology.
- Bond length variation drives the transition from semiconductor to semimetal.

## Abstract

Using angle resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations we studied the low-energy electronic structure of bulk ZrTe$_2$. ARPES studies on ZrTe$_2$ demonstrate free charge carriers at the Fermi level, which is further confirmed by the DFT calculations. An equal number of hole and electron carrier density estimated from the ARPES data, points ZrTe$_2$ to a semimetal. The DFT calculations further suggest a band inversion between Te $p$ and Zr $d$ states at the $\Gamma$ point, hinting at the non-trivial band topology in ZrTe$_2$. Thus, our studies for the first time unambiguously demonstrate that ZrTe$_2$ is a topological semimetal. Also, a comparative band structure study is done on ZrSe$_2$ which shows a semiconducting nature of the electronic structure with an indirect band gap of 0.9 eV between $\Gamma (A) $ and $M (L)$ high symmetry points. In the below we show that the metal-chalcogen bond-length plays a critical role in the electronic phase transition from semiconductor to a topological semimetal ingoing from ZrSe$_2$ to ZrTe$_2$.