Dissertations, Theses, and Capstone Projects
Date of Degree
9-2026
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy
Program
Physics
Advisor
Vinod Menon
Committee Members
Gabriele Grosso
Qiushi Guo
Alexander Khanikaev
Matthew Y. Sfeir
Subject Categories
Optics
Abstract
Exciton-polaritons, hybrid quasiparticles arising from strong light-matter coupling, provide a promising platform for realizing nonlinear and strongly interaction photonic systems. However, simultaneously achieving strong light–matter interactions, efficient photonic confinement, and external tunability remains a central challenge, motivating the search for new material platforms.
In this thesis, we investigate excitonic and polaritonic properties in the layered magnetic semiconductor CrSBr, a van der Waals material exhibiting strong in-plane anisotropy and pronounced exciton–magnon coupling. We demonstrate that CrSBr exhibits a highly anisotropic optical response for both excitons and polaritons, originating from its anisotropic crystal structure and excitonic dipole orientation. This enables low-loss, long-range polariton propagation over tens of micrometers with strong directionality along the crystal axes, together with suppressed transport along the orthogonal direction, resulting in effectively one-dimensional confinement. Furthermore, by embedding CrSBr flakes in a microcavity, the confinement is enhanced, leading to discretized modes along one direction and continuous dispersion along the other.
Beyond the anisotropic optical properties, we observe large magnetic-field-induced energy shifts of the excitonic resonances, originating from strong exciton–magnon coupling. These interactions manifest as magnon-mediated exciton–exciton interactions, leading to a pronounced and tunable nonlinear optical response. To harness this nonlinearity in a photonic platform, we explore cavity-based approaches for polariton formation. Conventional cavity designs suppress the effective nonlinear response due to fixed photonic modes. We overcome this limitation using photonic structures based on bound states in the continuum (BIC), where the photonic resonance dynamically tracks the excitonic energy, preserving the intrinsic nonlinearity while maintaining optical confinement. These results establish CrSBr as a unique platform that integrates strong light–matter interactions, optical anisotropy, magnetic tunability, and nonlinear optical response within a single material system, providing new opportunities for engineered polaritonic and photonic devices.
Recommended Citation
Yu, Sichao, "Exploring Excitonic Behavior and Polariton Dynamics in Crsbr: Insights into 2D Van Der Waals Magnetic Semiconductors" (2026). CUNY Academic Works.
https://academicworks.cuny.edu/gc_etds/6844
