Multiple Layer-Selective Polar Charge Density Waves in ${\rm{EuTe}}_{4}$

TL;DR

This study uncovers the layer-selective polar charge density wave nature in EuTe4, explaining its thermal hysteresis and non-volatile switching through first-principles calculations and Monte Carlo simulations, aligning with experimental data.

Contribution

It reveals the layer-selective nature of polar CDWs in EuTe4 and explains the giant thermal hysteresis and non-volatile switching mechanisms through theoretical modeling.

Findings

Layer-selective coexistence of multiple CDW configurations.

Giant thermal hysteresis driven by configurational entropy change.

Electric and optical fields can control the metastable CDW states.

Abstract

${\rm{EuTe}}_{4}$ is a polar charge density wave (CDW) material, with giant thermal hysteresis and non-volatile state switching under electric and optical fields, attracting great attention in recent years. However, the in-depth understanding of these anomalous phenomena remains elusive. Herein, via first-principles calculations, we reveal that the polar CDW state in ${\rm{EuTe}}_{4}$ hosts a novel layer-selective nature, wherein multiple energetically close CDW configurations coexist and exhibit low interconversion energy barriers. Monte Carlo simulations indicate that the giant thermal hysteresis in ${\rm{EuTe}}_{4}$ originates from a phase transition mainly driven by the change of configurational entropy, around which the material hosts a metastable CDW state characterized by diverse local polar configurations breaking the out-of-plane translational symmetry. The configurational composition of this metastable CDW state can be effectively controlled by electric and optical fields, thereby enabling non-volatile state switching. Our theoretical findings align well with recent experimental observations in ${\rm{EuTe}}_{4}$ and pave the way for exploring the emerging phenomena and applications of polar CDW in multilayered systems.