Exploiting the Spin Of Photons and Electrons in Light-Matter Interactions

2018-05
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Exploiting the Spin Of Photons and Electrons in Light-Matter Interactions

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2018-05

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In light-matter interaction, the conservation law of angular momentum requires the transfer of angular momentum of light to matter, which consequently couples light polarization to various state variables of materials, such as mechanical mo- tion, magnetization or charge current, thus gives rise to a plethora of intriguing physical phenomena. This dissertation focuses on the roles of photon spin and electron spin in light-matter interaction. Here, the angular momentum transfer in three different scenarios are studied. First, in an integrated optomechanical device, the spin angular momentum of light propagating in a waveguide is revealed through the use of optical torque to ex- cite torsional motion of the device. The quantitative optical torque measurement confirms the spin angular momentum of a photon in waveguide to be on the order of 􏰀. Our measurement also provides a check of the famous Minkowski-Abraham dilemma of photon angular momentum and verifies the Minkowski momentum applies in our system. Second, the coupling of light polarization and electron spin orientation is in- vestigated in the optical excitation of surface states in a 3D topological insu- lator Bi2Se3. The angular momentum conservation manifests itself in the spin- dependent optical selection rules and the generation of a photocurrent at zero bias voltage. Finally, we present the all-optical manipulation of magnetic order in ferrimag- netic alloy Gd(FeCo) using sub-picosecond laser pulses as the ultrafast stimuli. The instantaneous heating of the electron temperature due to light absorption triggers the energy and angular momentum exchange between the three thermo- dynamic reservoirs (electron, spin and lattice) and leads to the switching of mag- netization. As a step towards device application, we demonstrate an magnetic tunnel junction that can be switched all-optically without any external magnetic fields.

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University of Minnesota Ph.D. dissertation. 2018. Major: Physics. Advisor: Mo Li. 1 computer file (PDF); 124 pages.

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He, Li. (2018). Exploiting the Spin Of Photons and Electrons in Light-Matter Interactions. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/199071.

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