Theses and Dissertations

Advisor

Kim, Seong-Gon

Committee Member

Arnoldus, Henk

Committee Member

Novotny, Mark

Committee Member

Clay, R. Torsten

Committee Member

Gwaltney, Steven

Date of Degree

8-7-2025

Original embargo terms

Immediate Worldwide Access

Document Type

Dissertation - Open Access

Major

Physics

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Arts and Sciences

Department

Department of Physics and Astronomy

Abstract

We used first-principles density functional theory (DFT) to investigate the structural, electronic, and magnetic properties of an oxygen crystal in a copper slab, a ferrimagnetic electride with highly tunable magnetic anisotropy energy (MAE), and the Fermi surface analysis of different kagome metal phases. The Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional was used in the Vienna ab initio simulation package (VASP) for all these calculations. Because of dimensionality reduction, the electronic properties of copper change significantly at the two-dimensional (2D) scale due to whichwe observe more reconstruction in the geometry of the Fermi surface. Dimensionality reduction also influences charge transport. Moreover, we present the discovery of a novel 2D oxygen crystal, called "oxylene", on an ultraflat Cu(111) surface in a 4×4 periodicity confirmed by scanning tunneling microscopy (STM) and DFT studies. This crystal offers unique magnetization densities at the face-centered cubic (fcc) and hexagonal close packing (hcp) sites, with magnetic octupole moments attributed to oxygen atoms, and supports various linear responses, such as the piezoelectric effect and the magneto-optical Kerr effect, making it a universal platform in electronics and spintronics. In the second project, we study the structural, electronic, and magnetic properties of rare-earth metal-rich layered magnetic electrides and investigate the control of magnetism in the material. This material shows ferrimagnetic behavior with varying spin densities and excessively large MAE as a result of the interaction between interstitial anionic electron (IAEs) spin lattices and rare-earth f orbitals. We observe that the substitution of non-magnetic chlorine in IAE position leads to soft ferromagnetic ordering, which signifies that the IAE plays a prominent role in driving permanent magnetism. Our study entails new avenues into its spin structure and potential for tunable MAE in this material. In the third project, we investigate the structural and electronic properties of the kagome metal ScV6Sn6 with the help of band structure, Fermi surface, and phonon calculations in both pristine and charge density wave (CDW) phases. We observe that the square root of 3 by the square root of 3 by 3 CDW transition causes significant Fermi surface reconstruction because of periodic lattice distortion. To map the Fermi surface geometry, we measure the quantum oscillation frequencies with the help of the Fermi surface area that perfectly aligns with our experimental observations. Our study provides novel insights into the electronic properties, CDW order, and non-trivial topology of ScV6Sn6 and related vanadium-based kagome materials.

Download

Included in

Physics Commons

Share

COinS