Nonlinear THz emission spectroscopy of spin and charge dynamics in correlated materials

Understanding the intrinsic properties of materials is of fundamental importance to both scientific and technological advancements. The ability to characterize their electronic and optical behavior on the sub-picosecond timescale advances our understanding of the non-equilibrium physics and enables the development of next-generation applications in opto-electronis, spintronics and phase-change materials. This thesis is dedicated to investigate the charge and spin dynamics of correlated material systems upon optical illumination, with a special focus on their response in the terahertz (THz) frequency range. In this study, we examine FeRh, CrGeTe3, and Bi2Te3, which are materials of significant interest due to their unique electronic and magnetic properties. FeRh, known for its first-order metamagnetic phase transition, offers potential applications in heat-assisted magnetic recording. CrGeTe3, a layered ferromagnetic semiconductor, provides insights into two-dimensional magnetism and its potential in the ultimate dense storage platform. Bi2Te3, a well-known topological insulator, serves as a model system for studying topologically protected surface states and future error-tolerance quantum computing devices. To analyze these materials, we employ THz time-domain spectroscopy (TTDS), a technique that allows direct measurement of their complex optical response. By capturing both the amplitude and phase of THz waves, TTDS enables precise determination of essential parameters such as optical conductivity, refractive index, and carrier dynamics. This approach provides a powerful framework for probing phase transitions, charge transport mechanisms, and magnetic interactions in these systems. While the focus of this thesis remains on material properties, the methodological advancements in THz spectroscopy play a crucial role in unveiling the underlying physics of these complex systems. By bridging experimental techniques with condensed matter research, this work contributes to the growing field of THz spectroscopy in quantum materials. I extend my deepest gratitude to my advisors and colleagues who have guided and supported this research. I hope that the insights presented in this work will inspire further exploration into the fascinating properties of these novel materials.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Lu, Yinchuan

Contributors dc:contributor

• Mahmood, Fahad
• Bradlyn, Barry
• Hoffmann, Axel
• Wang, Pengjie

• Spectroscopy
• Terahertz
• Correlated Materials
• Magnetic materials
• Ultrafast optics
• Condensed matter physics

Statement dc:rights

• Copyright 2025 Yinchuan Lu

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129598

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129598