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

**Authors:** Abhishek Sharan, Stephan Lany, Nirpendra Singh  
**arXiv:** [2206.14626](https://arxiv.org/abs/2206.14626)  
**Date:** 2022-06-29  
**Summary page:** https://www.summarizepaper.com/en/paper/2206.14626v1/

## Key points

- Computational discovery of 2D rare-earth iodides (RI$_2$) for valleytronics
- Valleytronics utilizes valley degree of freedom in materials for information storage and processing
- Rare-earth iodides RI$_2$ identified as potential ferrovalley materials using Kinetically Limited Minimization (KLM)
- 17 new ferrovalley materials discovered in the form of rare-earth iodides RI$_2$
- Rare-earth iodides exhibit layered structures and can exist in different phases (2H, 1T, or 1T$_d$)
- Monolayers in the 2H phase demonstrate two-dimensional ferromagnetism
- $d$ bands exhibit intrinsic valley polarization at specific points in the Brillouin zone near Fermi level ($K$ and $\bar{K}$ points)
- Intrinsic valley polarization ranges from 15-143 meV and can be enhanced by applying biaxial strain
- Large intrinsic valley polarization makes these materials suitable for information storage and processing
- 2H ferromagnetic phase of RI$_2$ monolayers possesses non-zero Berry curvature and exhibits Valley Hall effect with considerable anomalous Hall conductivity
- Discovery opens up possibilities for synthesis and application in various fields such as long-range ferromagnetism, complex spin textures, optoelectronic properties, topological bands, and ferroelectricity

## Summary

In this study, the authors focus on the computational discovery of two-dimensional (2D) rare-earth iodides (RI$_2$), which are promising materials for valleytronics. Valleytronics is a field that utilizes the valley degree of freedom in materials to store and process information. While 2D materials with intrinsic valley polarization are highly desirable for valley-based nonvolatile random access memory and valley filters, they are relatively rare. To identify potential ferrovalley materials, the authors employed Kinetically Limited Minimization (KLM), an unconstrained crystal structure prediction algorithm, along with prototype sampling based on first-principles calculations. Through this approach, they discovered 17 new ferrovalley materials in the form of rare-earth iodides RI$_2$, where R represents a rare-earth element belonging to Sc, Y, or La-Lu, and I represents iodine. The rare-earth iodides exhibit layered structures and can exist in different phases such as 2H, 1T, or 1T$_d$ in bulk. These phases are analogous to transition metal dichalcogenides (TMDCs). The calculated exfoliation energy of monolayers is comparable to that of graphene and TMDCs, indicating the possibility of experimental synthesis. The monolayers in the 2H phase demonstrate two-dimensional ferromagnetism due to unpaired electrons in $d$ and $f$ orbitals. Interestingly, throughout the rare-earth series, $d$ bands exhibit valley polarization at specific points in the Brillouin zone near the Fermi level ($K$ and $\bar{K}$ points). This intrinsic valley polarization ranges from 15-143 meV without external stimuli and can be further tuned and enhanced by applying a biaxial strain. The large intrinsic valley polarization observed in these materials makes them suitable for selective probing and manipulation for information storage and processing; thus offering potential superior performance beyond conventional electronics and spintronics. Additionally, the authors found that the 2H ferromagnetic phase of RI$_2$ monolayers possesses non-zero Berry curvature which exhibits a Valley Hall effect with considerable anomalous Hall conductivity. The discovery of these new ferrovalley materials opens up possibilities for their synthesis and application in valleytronics as well as related fields such as long range ferromagnetism complex spin textures optoelectronic properties topological bands and ferroelectricity. Overall this study provides valuable insights into computational discovery of rare earth iodides as promising candidates for valley based electronic devices paving way for further exploration utilization of these materials towards various technological applications.