<p> This Dissertation presents the magneto-optical properties of monolayer (ML) transition metal dichalcogenide (TMDC) materials using our several magneto-optical setups that were developed at UB. In this Dissertation, we discuss a magneto-photoluminescence (PL) setup, a broadband magneto-FTIR setup, and a two-color spectroscopy setup in detail. We also discuss the double modulation technique, which we use in two-color spectroscopy. </p><p> The primary results of this work include magneto-PL measurements of ML WSe<sub>2</sub> on YIG. We pump these materials with circularly polarized light and analyze with a circular polarizer. We reported a 30% polarization and 10 nm peak shift in a localized state with an applied magnetic field. We see a polarization up to T = 80 K. By changing the magnetic field from –7 Tesla to +7 Tesla, localized impurity-bound exciton states show strong polarization under optical excitation of opposite helicity. Right circularly polarized PL peaks are shifted to lower energies and their PL become stronger than left circularly polarized PL peaks. This is opposite for left circularly polarized peaks. They shift to higher energies (shorter wavelengths) and become weaker than right circularly polarized peaks. We also found that localized states show more polarization than free exciton and trion peaks on YIG substrate. </p><p> We also investigated Kerr rotation and Kerr ellipticity properties of ML MoS<sub>2</sub> and ML WSe<sub>2</sub> on YIG with our new broadband magneto—FTIR optical setup. Samples and substrate do not show any Kerr ellipticity features when exposed to a changing magnetic field. All samples show strong magnetic field dependent Kerr rotation signal but we found that ML MoS<sub>2</sub> by itself does not show any magnetic field dependent Kerr rotation signal. We found that there are two broad peaks in the YIG and ML WSe<sub>2</sub> on YIG Kerr rotation spectrum. YIG’s two broad peak centers are located at around 1800 cm<sup>–1</sup> and 2300 cm<sup>–1</sup> and ML WSe<sub>2</sub> on YIG peak centers are located at around 1900 cm<sup> –1</sup> and 2500 cm<sup>–1</sup>. For both samples, these peak intensities are linear with the magnetic field and they are symmetric with respect to B = 0 T. ML WSe<sub>2</sub> on YIG peaks are shifted to higher energies with respect to YIG peak. We also report that the center of the peaks has no shift with a magnetic field. </p><p> With our two-color spectroscopy setup, we have tested Imamoglu’s theory that predicts a splitting of dark 2p states at B = 0 Tesla. A circularly polarized laser and a linearly polarized IR laser were used together to excite electrons to dark states. We used red or green laser and CO or CO<sub>2</sub> IR laser together in our experimental setup. Samples are ML MoS<sub>2</sub> on sapphire and ML WS<sub>2</sub> on Si/SiO<sub>2</sub>. Within a sensitivity of 10 µrad, we did not see any splitting at B = 0 Tesla on any samples.</p><p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:13427593 |
| Date | 21 March 2019 |
| Creators | Arik, Mumtaz Murat |
| Publisher | State University of New York at Buffalo |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
Page generated in 0.0016 seconds