Kaifa Luo Thesis Defense

Abstract: Emergent quasiparticles in solids often exhibit unique topological properties as a result of the complex interplay between charge, orbital, spin and lattice degrees of freedom. Among these quasiparticles, the polaron occupies a special place as the first known manifestation of the interaction between a fermion and a boson field. While polarons have been investigated for almost a century, whether these quasiparticles exhibit topological properties and why remain open questions. Here, we establish the universal symmetry principles governing the topology of polar textures in large polarons. Using a group-theoretic analysis, we identify four distinct classes of polar textures carrying integer topological charges. In addition to the topological patterns associated with the ground states, we also explore the excited states of polarons and identify hydrogen-like spectrum and wave functions. We validate our theory by performing state-of-the-art first-principles calculations of representative materials. For these materials, we make connections between the topology and excitation with Huang diffuse scattering and infrared absorptions, respectively.