School of Physics Thesis Dissertation Defense

Presenter:        Olivia Viella

Title:                     Novel Magnetic Phases of Quantum Matter from Geometric, Spin-Space and Chemical Frustration

Date:                    Tuesday, July 2, 2024

Time:                    10:30 a.m. 

Location:           Howey Physics Building, N201/202

Committee members: 

Dr. Martin Mourigal, School of Physics, Georgia Institute of Technology (advisor)

Dr. Claire Berger, School of Physics, Georgia Institute of Technology 

Dr. Zhigang Jiang, School of Physics, Georgia Institute of Technology 

Dr. Itamar Kimchi, School of Physics, Georgia Institute of Technology

Dr. Joe Paddison, Neutron Scattering Division, Oak Ridge National Laboratory 

Abstract:

Quantum magnetism is a branch of hard condensed matter physics concerned with realizing, understanding, and controlling novel quantum phases of matter. The chemical and geometrical differences in the crystal lattices of various transition-metal and rare-earth compounds lead to complex magnetic phenomena, which offer a vast arena for investigating quantum magnetism using theoretical and experimental tools. This thesis presents work on both heavily studied and new candidate materials to realize exotic magnetic states of matter. Experimental methods, including thermomagnetic measurements and inelastic neutron scattering, were paired with semi-classical methods to model spin dynamics to characterize the ground-state and excitation spectrum of three distinct systems. The work on the triangular-lattice material YbMgGaO4 evidences the combined role of geometric and chemical frustration to stabilize a disorder spin state on the triangular lattice. Thermomagnetic experiments on the quantum pyrochlore antiferromagnet LiYbSe2 indicate missing entropy implying a possible spin-ice phase, which neutron diffraction confirming magnetic isotropy. The work on the magnetic skyrmion candidate NiI2 show the first experimental evidence of a high-topological skyrmion which is not stabilized by a DM or RKKY interaction in a magnetic field; but rather, but Kitaev exchange.