Date of Award

Winter 2020

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Jiadong Zang

Second Advisor

Per Berglund

Third Advisor

Shawna Hollen

Abstract

Emergence of quasiparticles is a central concept in condensed matter physics. As an example, in solids, lattice vibrations lead to quantized phonon excitations, which gives rise to many exotic phenomena, including superconductivity. Things become richer in magnetic systems. Collective fluctuations about a magnetic ground state induce the spin wave excitation, whose quantized quasiparticle is dubbed as the magnon. A fundamental question is how phonon and magnon, as two separate degrees of freedom, can be coupled together. More importantly, certain symmetry, such as spatial inversion symmetry, can be broken in novel magnetic textures. It is interesting to explore whether broken symmetry in spin systems can be manifested in lattice vibrations through the coupling between magnon and phonon. In this dissertation work, I studied the microscopic mechanism of magnon-phonon coupling known as magnetoelastic coupling. Using a comoving coordinate technique, I systematically analyzed the spin wave excitation out of various ground states in chiral magnetic spin models. By solving highly entangled differential equations, I showed spin waves can be excited by lattice vibrations via magnetoelastic coupling. Furthermore, nonreciprocal propagation of elastic and magnetic waves was found once the magnetoelastic coupling is turned on. At low temperature regimes where spin wave quantization becomes important and magnons are emergent, I discovered transverse deflection of magnon propagation, dubbed the magnon Hall effect, driven by the magnetoelastic coupling. This work sheds light on future pump probe experiments in unlocking spin interactions via lattice vibrations.

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