Polaronic and Mott insulating phase of layered magnetic vanadium trihalide VCl3

TL;DR

This paper investigates the electronic, magnetic, and structural properties of 2D vanadium trichloride (VCl3), revealing its Mott insulating state, phase transitions, and the role of magnetic polarons in its physical behavior.

Contribution

It provides the first detailed synthesis, characterization, and theoretical analysis of VCl3 as a layered Mott insulator with polaronic effects influencing its properties.

Findings

VCl3 is a 2D layered Mott insulator with a rhombohedral structure.

It undergoes structural and antiferromagnetic phase transitions at 103 K and 21.8 K.

Magnetic polarons localized on V sites significantly affect the electromagnetic properties.

Abstract

Two-dimensional (2D) van der Waals (vdW) magnetic $3d$-transition metal trihalides are a new class of functional materials showing exotic physical properties useful for spintronic and memory storage applications. In this article, we report the synthesis and electromagnetic characterization of single-crystalline vanadium trichloride, VCl$_3$, a novel 2D layered vdW Mott insulator, which has a rhombohedral structure (R$\overline{3}$, No. 148) at room temperature. VCl$_3$ undergoes a structural phase transition at 103 K and a subsequent antiferromagnetic transition at 21.8 K. Combining core levels and valence bands x-ray photoemission spectroscopy (XPS) with first-principles density functional theory (DFT) calculations, we demonstrate the Mott Hubbard insulating nature of VCl$_3$ and the existence of electron small 2D magnetic polarons localized on V atom sites by V-Cl bond relaxation. The polarons strongly affect the electromagnetic properties of VCl$_3$ promoting the occupation of dispersion-less spin-polarized V-3d $a_{1g}$ states and band inversion with $e^{'}_{g}$ states. Within the polaronic scenario, it is possible to reconcile different experimental evidences on vanadium trihalides, suggesting that also VI$_3$ hosts polarons. Our results highlight the complex physical behavior of this class of crystals determined by charge trapping, lattice distortions, correlation effects, mixed valence states, and magnetic states.