Beyond linear responses: exploring magnetic materials through nonlinear terahertz spectroscopy

Murzabekova, Azel

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https://hdl.handle.net/2142/129719 Copy

Description

Title

Beyond linear responses: exploring magnetic materials through nonlinear terahertz spectroscopy

Author(s)

Murzabekova, Azel

Issue Date

2025-04-25

Director of Research (if dissertation) or Advisor (if thesis)

Mahmood, Fahad

Doctoral Committee Chair(s)

Vishveshwara, Smitha

Committee Member(s)

• Cooper, Lance
• Hoffmann, Axel

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Terahertz spectroscopy
• magnetism

Abstract

Michael Faraday’s unsuccessful attempts to observe the polarization rotation of light through a transparent insulator under the influence of a strong electric field prompted him to test the same experiment with a magnetic field. Thirty years later, Rev. John Kerr repeated Faraday’s experiments with more sensitive equipment and observed what we now know as the electro-optic effect and magneto-optic Kerr effect. These discoveries opened a new era of research in magnetism, and to this day, the magneto-optic effect is one of the simplest, yet most powerful tools to characterize magnetic materials. The goal of this thesis is to explore linear and nonlinear responses of magnetic materials using static Kerr and terahertz spectroscopies. We carefully analyze different contributions to the polarization rotation of light reflected from magnetic materials and demonstrate how to disentangle them using a custom-built variable-polarization static Kerr spectrometer. Moving beyond conventional linear responses, we demonstrate how nonlinear terahertz spectroscopy serves as a powerful probe of complex electronic states in magnetic systems. Specifically, we investigate the antiferromagnetic metal Fe1/3NbS2, where intense terahertz electric fields cause a nonlinear electro-optical response. This behavior provides evidence for electronic nematicity - a state where electronic properties break rotational symmetry while preserving translational symmetry. Furthermore, we extend our terahertz spectroscopic studies to explore collective excitations in exotic quantum materials, focusing on potential quantum spin liquid candidates Ba4Ir3O10 and CsYbSe2. These materials, characterized by strong quantum fluctuations that prevent conventional magnetic ordering, offer a fascinating platform for studying novel quantum states of matter. Through the combination of these advanced spectroscopic techniques, our research unveils previously hidden phenomena in magnetic materials with complex interactions. The insights gained contribute to both fundamental understanding of quantum materials and potential applications in emerging quantum technologies, from information processing to sensing. This work demonstrates the continuing relevance of magneto-optical techniques, first pioneered by Faraday and Kerr, in modern materials research, while show- casing how their integration with cutting-edge terahertz spectroscopy opens new avenues for investigating quantum materials. Beyond the linear response, we also show how nonlinear terahertz spectroscopy can be used to probe complex electronic states in the antiferromagnetic metal Fe1/3NbS2. Strong terahertz electric fields induce a nonlinear optical response in this material, which was attributed to the presence of nematicity. Finally, we also show how terahertz radiation can be used to probe excitations in unusual magnetic materials, such as quantum spin liquid candidates Ba4Ir3O10 and CsYbSe2. Overall, this research demonstrates how advanced spectroscopic techniques can reveal hidden phenomena in materials with complex magnetic interactions, providing insights into fundamental physics and potential applications in quantum technologies.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129719

Copyright and License Information

Copyright 2025 Azel Murzabekova

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