Ferroelectric Control of Topological Properties of Two-Dimensional Materials

Author

Kai Huang, University of Nebraska-LincolnFollow

Date of Award

Spring 2024

Document Type

Dissertation

Department

Physics and Astronomy

First Advisor

Evgeny Tsymbal

Abstract

Topological characteristics, such as magnetic quasiparticles like skyrmions, and the presence of anomalous and quantum Hall effects, have significantly propelled the field of spintronics. The recent discovery of two-dimensional (2D) ferroic materials opens up a novel platform for incorporating these properties within atomic-thin layers, offering potential advancements in the creation of compact spintronic devices. This dissertation focuses on the exploration of topological features of 2D van der Waals (vdW) materials through first-principles density functional theory calculations. The formation of magnetic skyrmions in 2D vdW ferromagnet Fe₃GeTe₂ driven by proximity of 2D ferroelectric In2Se3 are studied. The interfacial symmetry breaking produces a sizable Dzyaloshinskii-Moriya interaction (DMI) in a Fe₃GeTe₂/In₂Se₃ vdW heterostructure. The magnitude of DMI can be controlled by ferroelectric polarization reversal, leading to creation and annihilation of skyrmions. Additionally, the sign of DMI in a In₂Se₃/Fe₃GeTe₂/In₂Se₃ heterostructure changes with ferroelectric switching, thereby reversing the chirality of the skyrmions. The emergence of an anisotropic DMI and formation of magnetic antiskyrmions in a vdW assembled 2D magnet CrI3 are studied. Polar layer stacking of two monolayers of CrI3 efficiently lowers the symmetry, resulting in the anisotropic DMI. The DMI is reversible by switching the ferroelectric polarization inherited from the polar layer stacking, offering the control of antiskyrmions by an electric field. Spin-dynamics simulations of a Mn doped CrI₃ bilayer with reduced magnetocrystalline anisotropy demonstrate the formation of antiskyrmions and the switching of their spin texture with ferroelectric polarization reversal. The anomalous Hall effect (AHE) is explored in antiferromagnetic MnBi₂Te₄ films assembled by polar layer stacking. The breaking of P ̂T ̂symmetry in an MnBi₂Te₄ bilayer renders this 2D material magnetoelectric, leading to a spontaneous AHE that can be switched by electric polarization. In a three-layer MnBi₂Te₄ film, the reversible polarization at one of the interfaces induces a metal-insulator transition, facilitating switching between the AHE and quantum AHE (QAHE). Furthermore, the polarization in a three-layer MnBi₂Te₄ film enables converting MnBi₂Te₄ from a trivial insulator to a Chern insulator.

Comments

Copyright 2024, Kai Huang. Used by permission

Recommended Citation

Huang, Kai, "Ferroelectric Control of Topological Properties of Two-Dimensional Materials" (2024). Dissertations and Doctoral Documents from University of Nebraska-Lincoln, 2023–. 108.
https://digitalcommons.unl.edu/dissunl/108