Computational Discovery of Two-Dimensional Rare-Earth Iodides: Promising Ferrovalley Materials for Valleytronics

TL;DR

This paper reports the computational discovery of 17 new two-dimensional rare-earth iodide materials with intrinsic valley polarization and ferromagnetism, promising for valleytronics applications such as nonvolatile memory and valley filters.

Contribution

The study introduces a novel computational approach combining Kinetically Limited Minimization and first-principles calculations to predict new Ferrovalley materials with tunable valley polarization.

Findings

Discovered 17 new rare-earth iodide Ferrovalley materials.

Monolayers exhibit large intrinsic valley polarization (15-143 meV).

Predicted valley Hall effect and non-zero Berry curvature in 2H phase monolayers.

Abstract

Two-dimensional Ferrovalley materials with intrinsic valley polarization are rare but highly promising for valley-based nonvolatile random access memory and valley filter. Using Kinetically Limited Minimization (KLM), an unconstrained crystal structure prediction algorithm, and prototype sampling based on first-principles calculations, we have discovered 17 new Ferrovalley materials (rare-earth iodides RI$_2$, where R is a rare-earth element belonging to Sc, Y, or La-Lu, and I is Iodine). The rare-earth iodides are layered and demonstrate 2H, 1T, or 1T$_d$ phase as the ground-state in bulk, analogous to transition metal dichalcogenides (TMDCs). The calculated exfoliation energy of monolayers is comparable to that of graphene and TMDCs, suggesting possible experimental synthesis. The monolayers in the 2H phase exhibit two-dimensional ferromagnetism due to unpaired electrons in $d$ and $f$ orbitals. Throughout the rare-earth series, $d$ bands show valley polarization at $K$ and $\bar{K}$ points in the Brillouin zone near the Fermi level. Due to strong magnetic exchange interaction and spin-orbit coupling, large intrinsic valley polarization in the range of 15-143 meV without external stimuli is observed, which can be tuned and enhanced by applying a biaxial strain. These valleys can selectively be probed and manipulated for information storage and processing, potentially offering superior performance beyond conventional electronics and spintronics. We further show that the 2H ferromagnetic phase of RI$_2$ monolayers possesses non-zero Berry curvature and exhibits the valley Hall effect with considerable anomalous Hall conductivity. Our work will incite exploratory synthesis of the predicted Ferrovalley materials and their application in valleytronics and beyond.