Nonlinear Optical Studies on Two-Dimensional Antiferromagnets and Topological Semimetals / Zhuoliang Ni.

Format:

Book

Thesis/Dissertation

Author/Creator:

Ni, Zhuoliang, author.

Contributor:

University of Pennsylvania. Physics and Astronomy, degree granting institution.

Language:

English

Subjects (All):

Physics.

Electromagnetics.

Materials science.

Physics and Astronomy--Penn dissertations.

Penn dissertations--Physics and Astronomy.

Local Subjects:

Physics.

Electromagnetics.

Materials science.

Physics and Astronomy--Penn dissertations.

Penn dissertations--Physics and Astronomy.

Physical Description:

1 online resource (116 pages)

Distribution:

Ann Arbor : ProQuest Dissertations & Theses, 2023

Contained In:

Dissertations Abstracts International 85-08B.

Place of Publication:

[Philadelphia, Pennsylvania] : University of Pennsylvania, 2022.

Language Note:

English

Summary:

This thesis presents a study of van der Waals antiferromagnetic materials and topological semimetals, examining their quantum behavior through optical nonlinear harmonic generation and terahertz emission techniques. We specifically investigated spin behaviors at low dimension in transition metal trichalcogenides MPX3 and explored nonlinear optical responses and quantized photogalvanic effects in multi-fold semimetals RhSi and CoSi.We developed an ultra-high sensitivity second-harmonic generation microscope, capable of detecting 0.1 photon per second, which allowed us to characterize antiferromagnetic orders at the single-layer limit. Additionally, we established a broadband terahertz emission setup with an excitation energy range of 0.2 eV to 1.5 eV at cryogetic temperature. This mid-IR capacity facilitated the detection of topological responses within the Weyl cones of the materials.Utilizing the second-harmonic generation microscope, we imaged antiferromagnetic orders in two-dimensional magnetic materials, such as Neel-type MnPSe3 and MnPS3, and zigzag-type FePS3. MnPSe3 is a van der Waals antiferromagnet with in-plane Neel orders, and we detected its antiferromagnetic long-range ordering down to the monolayer limit through optical second-harmonic generation. MnPS3 is another van der Waals antiferromagnet with out-of-plane Neel orders and exhibits nearly isotropic magnetic anisotropy, closely resembling a Heisenberg magnet. We demonstrated long-range order in bilayer samples but observed suppressed magnetism in monolayer samples. By exploiting the interference between two distinct second-harmonic terms, we successfully imaged the different domains in both materials. Unlike MnPSe3 and MnPS3, the zigzag orders in FePS3 did not break inversion symmetry; however, its antiferromagnetism was strongly coupled to the surface second-harmonic generation, enabling detection of zigzag orders in few-layer samples.We investigated the unique properties of the XY magnet MnPSe3 with in-plane spins, where polarization-resolved measurements resolved the in-plane spin direction of the samples. We discovered that the spin direction was pinned by small, arbitrary local strain, and it could be further manipulated by additional magnetic anisotropy induced by strain control or in-plane magnetic fields. Our findings highlight the XY nature of intrinsic MnPSe3 samples and the stabilization of long-range order in 2D due to external anisotropy from the environment.Lastly, we investigated topological materials with noncentrosymmetric structures. We detected topological photogalvanic effects near a single topological node through terahertz emission, extending down to mid-IR photon excitation. We studied the relationship between the magnitude of nonlinear optical responses and topological electronic structures, and with the assistance of density functional theory, we examined the topological origins of photogalvanic effects and the proposed quantized circular photogalvanic effects.

Notes:

Source: Dissertations Abstracts International, Volume: 85-08, Section: B.

Advisors: Wu, Liang; Committee members: Mele, Eugene; Kikkawa, Jay; Klein, Joshua R.; Claassen, Martin.

Department: Physics and Astronomy.

Ph.D. University of Pennsylvania 2023.

Local Notes:

School code: 0175

ISBN:

9798381471649

Access Restriction:

Restricted for use by site license.