Small polarom formation by electron-electron interaction

TL;DR

This paper demonstrates that in 2D transition metal halides, electron-electron interactions can induce polaron formation without lattice distortion, revealing a new mechanism for carrier localization in strongly correlated systems.

Contribution

It introduces a novel electron-electron interaction-driven polaron formation mechanism in 2D materials, supported by first-principles calculations and experimental STM/STS evidence.

Findings

Electron-electron interactions can form polarons without lattice distortion.

First-principles calculations confirm polaron formation in CrI2, CoCl2, CoBr2.

STM/STS measurements observe polarons in CrI2.

Abstract

In a solid, electrons can be scattered both by phonons and other electrons. First proposed by Landau, scattering by phonons can lead to a composite entity called a polaron, in which a lattice distortion traps an itinerant electron (or hole) such that the distortion and carrier move in unison as a single particle with larger effective mass. While this is the traditional view of polarons, the rise of 2D systems, especially strongly correlated ones, open the prospect of electron scattering taking on a larger role in spontaneous carrier localization for such material systems. Here, we show that in transition metal halides, such electron-electron interactions can lead to polaron formation even in the absence of lattice distortion. This suggests an alternative direction for polaron formation, transport, and control in solids. This new mechanism of polaron formation is confirmed by first-principles calculation of 2D transition metal halides, CrI2, CoCl2 and CoBr2. These theoretical predictions are supported by scanning tunneling microscopy/spectroscopy measurements of polarons in CrI2.