{"id":{"repo_id":"buffalo","oai_identifier":"oai:ubir.buffalo.edu:10477/80852"},"canonical_url":"https://search.dev.ndltd.org/etd/buffalo/oai:ubir.buffalo.edu:10477/80852","repository":{"repo_id":"buffalo","name":"Buffalo","base_url":"https://ubir.buffalo.edu/oai/request"},"display":{"title":"Magneto Optical Studies of Two Dimensional Transition Metal Dichalcogenides","abstract":"Ph.D.","abstract_html":"Ph.D.","abstract_has_math":false,"creators":["Norden, Tenzin"],"institution":"State University of New York at Buffalo","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Petrou, Athos","Physics"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2019,"date_issued":"2019-10-29T16:47:33Z","date_published":"2019-10-29T16:47:33Z","updated_at":"2026-07-27T19:05:25Z","subjects":["physics"],"languages":["eng"],"rights":["Users of works found in University at Buffalo Institutional Repository (UBIR) are responsible for identifying and contacting the copyright owner for permission to reuse. University at Buffalo Libraries do not manage rights for copyright-protected works and cannot assist with permissions.","Copyright retained by author."],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/10477/80852","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Petrou, Athos","Physics"]},{"key":"dc:creator","label":"Author","values":["Norden, Tenzin"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2019-10-29T16:47:33Z","2019","2019-07-18 15:02:58"]},{"key":"dc:publisher","label":"Institution","values":["State University of New York at Buffalo"]},{"key":"dc:type","label":"Dc Type","values":["Text","Dissertation"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["physics"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Users of works found in University at Buffalo Institutional Repository (UBIR) are responsible for identifying and contacting the copyright owner for permission to reuse. University at Buffalo Libraries do not manage rights for copyright-protected works and cannot assist with permissions.","Copyright retained by author."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/10477/80852"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Ph.D.","This dissertation is about magneto-optical studies of valley Zeeman splitting in the heterostructures of monolayer transition metal dichalcogenides (WSe2 and WS2) on a ferromagnetic EuS substrate due to interfacial magnetic exchange field (MEF). A monolayer TMD with a broken inversion symmetry possesses two degenerate but inequivalent K and K’ valleys, which offers unique opportunities for valley control through the helicity of light. When external magnetic field is applied in the direction perpendicular to the sample, the valley degeneracy can be lifted. Lifting of the valley degeneracy of monolayer TMDs may enable valley control by a magnetic field. However, the realized valley splitting is small at about ~0.2 meV/T, not desired for any valleytronic applications. Our motivation here is to enhanced the valley splitting by magnetic proximity effect. We created heterostructures of WSe2/EuS and WS2/EuS and used various experimental techniques, including magneto-reflectivity, to study properties of TMDs. I present our experimental results on two projects based on magnetic proximity effect induced by MEF. Utilizing the MEF of a magnetic insulator can induce magnetic order and, valley and spin polarization in TMDs, which may enable valleytronics and quantum-computing applications. In the first project, we have demonstrated greatly enhanced valley splitting in monolayer WSe2 by utilizing the interfacial MEF from a ferromagnetic EuS substrate. A valley splitting of ~2.5 meV is demonstrated at 1 T by magneto-reflectance measurements which corresponds to an effective exchange field of ~12T. Moreover, the splitting follows the magnetization of EuS, a hallmark of the MEF. In the second project, we report a giant valley exciton splitting of ~ -16 meV/T for monolayer WS2, using the proximity effect from a ferromagnetic EuS substrate, which is enhanced by nearly two orders of magnitude from the 0.2 meV/T obtained by an external magnetic field. More interestingly, a sign reversal of the valley exciton splitting is observed as compared to that of WSe2 on EuS. Using first principles calculations, we investigate the complex behavior of exchange interactions between TMDs and EuS, that is qualitatively different from the Zeeman effect. The sign reversal is attributed to competing ferromagnetic (FM) and antiferromagnetic (AFM) exchange interactions for Eu- and S- terminated EuS surface sites. They act differently on the conduction and valence bands of WS2 compared to WSe2. This creates a possibility of tuning the sign and magnitude of the valley exciton splitting, offering opportunities for versatile control of valley pseudospin for quantum information processing."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Magneto Optical Studies of Two Dimensional Transition Metal Dichalcogenides"]}]}],"canonical_facts":{"dc:contributor":["Petrou, Athos","Physics"],"dc:creator":["Norden, Tenzin"],"dc:date":["2019-10-29T16:47:33Z","2019","2019-07-18 15:02:58"],"dc:description":["Ph.D.","This dissertation is about magneto-optical studies of valley Zeeman splitting in the heterostructures of monolayer transition metal dichalcogenides (WSe2 and WS2) on a ferromagnetic EuS substrate due to interfacial magnetic exchange field (MEF). A monolayer TMD with a broken inversion symmetry possesses two degenerate but inequivalent K and K’ valleys, which offers unique opportunities for valley control through the helicity of light. When external magnetic field is applied in the direction perpendicular to the sample, the valley degeneracy can be lifted. Lifting of the valley degeneracy of monolayer TMDs may enable valley control by a magnetic field. However, the realized valley splitting is small at about ~0.2 meV/T, not desired for any valleytronic applications. Our motivation here is to enhanced the valley splitting by magnetic proximity effect. We created heterostructures of WSe2/EuS and WS2/EuS and used various experimental techniques, including magneto-reflectivity, to study properties of TMDs. I present our experimental results on two projects based on magnetic proximity effect induced by MEF. Utilizing the MEF of a magnetic insulator can induce magnetic order and, valley and spin polarization in TMDs, which may enable valleytronics and quantum-computing applications. In the first project, we have demonstrated greatly enhanced valley splitting in monolayer WSe2 by utilizing the interfacial MEF from a ferromagnetic EuS substrate. A valley splitting of ~2.5 meV is demonstrated at 1 T by magneto-reflectance measurements which corresponds to an effective exchange field of ~12T. Moreover, the splitting follows the magnetization of EuS, a hallmark of the MEF. In the second project, we report a giant valley exciton splitting of ~ -16 meV/T for monolayer WS2, using the proximity effect from a ferromagnetic EuS substrate, which is enhanced by nearly two orders of magnitude from the 0.2 meV/T obtained by an external magnetic field. More interestingly, a sign reversal of the valley exciton splitting is observed as compared to that of WSe2 on EuS. Using first principles calculations, we investigate the complex behavior of exchange interactions between TMDs and EuS, that is qualitatively different from the Zeeman effect. The sign reversal is attributed to competing ferromagnetic (FM) and antiferromagnetic (AFM) exchange interactions for Eu- and S- terminated EuS surface sites. They act differently on the conduction and valence bands of WS2 compared to WSe2. This creates a possibility of tuning the sign and magnitude of the valley exciton splitting, offering opportunities for versatile control of valley pseudospin for quantum information processing."],"dc:format":["application/pdf"],"dc:identifier":["http://hdl.handle.net/10477/80852"],"dc:language":["eng"],"dc:publisher":["State University of New York at Buffalo"],"dc:rights":["Users of works found in University at Buffalo Institutional Repository (UBIR) are responsible for identifying and contacting the copyright owner for permission to reuse. University at Buffalo Libraries do not manage rights for copyright-protected works and cannot assist with permissions.","Copyright retained by author."],"dc:subject":["physics"],"dc:title":["Magneto Optical Studies of Two Dimensional Transition Metal Dichalcogenides"],"dc:type":["Text","Dissertation"]},"updated_at":"2026-07-27T19:05:25Z"}