# Layered semiconductor EuTe 4 with charge density wave order in square tellurium sheets

## TL;DR

This paper reports a new quasi-two-dimensional EuTe4 compound exhibiting charge density wave order, structural phase transition, and semiconducting behavior, providing insights into 2D semiconductors with collective electronic states.

## Contribution

The study introduces a novel EuTe4 compound with charge density wave order and detailed structural and electronic characterization, advancing understanding of 2D CDW systems.

## Key findings

- Charge density wave order observed below 255 K.
- Structural superstructure with Te-trimers formation.
- Semiconducting behavior in the CDW state.

## Abstract

We report a novel quasi-two dimensional compound of EuTe4 hosting charge density waves (CDW) instability. The compound has a crystallographic structure in a orthorhombic space group Pmmn (No.59) with cell parameters a = 4.6347(2){\AA}, b = 4.5119(2){\AA}, c = 15.6747(10){\AA} at room temperature. The pristine structure contains consecutive near-square Te sheets separated by corrugated Eu-Te slabs. Upon cooling, the compound experiences a phase transition near 255 K. X-ray crystallographic analysis and transmission electron microscopy (TEM) measurements reveal strong structural distortions in the low temperature phase, showing a superstructure with a periodic formation of Te-trimers in the monolayer Te sheets, yielding evidence for the formation of CDW order. The charge transport properties show a semiconducting behavior in the CDW state. Density functional theory calculations reveals a Fermi surface nesting driven instability with a nesting vector in good agreement with the one observed experimentally. Our finding provides a promising system for the study of CDW driven 2D semiconducting mechanisms, which would shed a new light on exploring novel 2D semiconductors with collective electronic states.