The anti-distortive polaron : an alternative mechanism for lattice-mediated charge trapping

TL;DR

This paper introduces the concept of anti-distortive polarons, a new mechanism for lattice-mediated charge trapping in materials like WO$_3$, based on advanced first-principles calculations that challenge traditional models.

Contribution

It presents the novel concept of anti-distortive polarons, explaining their formation and properties through a quantum-dot model, expanding understanding beyond classical polaron theories.

Findings

Anti-distortive polarons lower the bandgap via dynamical covalency effects.

This mechanism is observed in WO$_3$ and is applicable to other compounds.

The concept offers new avenues for controlling polaronic states in materials.

Abstract

Polarons can naturally form in materials from the interaction of extra charge carriers with the atomic lattice. Ubiquitous, they are central to various topics and phenomena such as high-T$_c$ superconductivity, electrochromism, photovoltaics, photocatalysis or ion batteries. However, polaron formation remains poorly understood and mostly relies on few historical models such as Landau-Pekar, Fr\"olich, Holstein or Jahn-Teller polarons. Here, from advanced first-principles calculations, we show that the formation of intriguing medium-size polarons in WO$_3$ does not fit with traditional models but instead arises from the undoing of distortive atomic motions inherent to the pristine phase, which lowers the bandgap through dynamical covalency effects. We so introduce the innovative concept of {\it anti-distortive} polaron and rationalize it from a quantum-dot model. We demonstrate that anti-distortive polarons are generic to different families of compounds and clarify how this new concept opens concrete perspectives for a better control of the polaronic state and related properties.