{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/384254"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/384254","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Quantum oscillations in Dirac semimetals","abstract":"Dirac semimetals have recently gained interest due to their unique experimental signatures many of which can be explained by the topologically non-trivial band structure in these materials. Among the many candidates, the tellurides NbTe₄, TaPtTe₅ and TaNiTe₅ appear to provide a promising platform for the study of such topological properties. To probe their band structure and its corresponding Fermi surface, quantum oscillations have proven very useful as they provide a tool to directly measure the Berry phase under certain conditions. The (double) Dirac semimetal NbTe₄ has shown the occurrence of multiple charge-density-wave (CDW) phases, and as a result a complex band structure at low temperatures. Density functional theory (DFT) calculations predict the presence of an eight-fold degenerate band crossing whose topological properties are investigated in this thesis. The magnetoresistance in this material shows the onset of linear behaviour at 15 T which indicates the presence of Dirac-like band crossings, while the angular magnetoresistance (AMR) measurements also resemble results known from topological semimetals, however alternative explanations seem more likely to explain these results in NbTe₄. Experimental signatures expected from Dirac semimetals are further examined with a comprehensive study of the magnetic torque anomaly, and by measuring de Haas - van Alphen (dHvA) oscillations in the magnetic torque and Shubnikov - de Haas (SdH) oscillations in the magnetoresistance. Combined with DFT calculations, quantum oscillations allow to map the Fermi surface of this material. Furthermore, non-trivial Berry phases and low effective masses can be observed together with high frequencies that could either be the remains of a different CDW phase or arise from magnetic breakdown. Based on symmetry arguments of the crystal structure, the Dirac nodal-line semimetal candidate TaPtTe₅ is theoretically predicted to host four-fold degenerate lines with linear band dispersion in reciprocal space. The work presented here aims at confirming the theoretical predictions by providing a numerical investigation of the band structure and comparing that to results from dHvA oscillations in the magnetic torque. Closely related to TaPtTe₅, the structurally similar compound TaNiTe₅ is also predicted to host Dirac nodal-lines. Again, quantum oscillations in the magnetic torque are used to obtain insights into the morphology of the Fermi surface, while effective masses can be extracted from temperature-dependent dHvA measurements in the magnetisation. Unlike other semimetals reported in the literature, TaNiTe₅ furthermore shows enhanced oscillations in the magnetoresistance, even in the out-of-phase component of the applied alternating current. A thorough investigation of this effect is performed and a numerical model can explain the effect within the framework of classical electrodynamics without involvement of topological physics.","abstract_html":"Dirac semimetals have recently gained interest due to their unique experimental signatures many of which can be explained by the topologically non-trivial band structure in these materials. Among the many candidates, the tellurides NbTe₄, TaPtTe₅ and TaNiTe₅ appear to provide a promising platform for the study of such topological properties. To probe their band structure and its corresponding Fermi surface, quantum oscillations have proven very useful as they provide a tool to directly measure the Berry phase under certain conditions. The (double) Dirac semimetal NbTe₄ has shown the occurrence of multiple charge-density-wave (CDW) phases, and as a result a complex band structure at low temperatures. Density functional theory (DFT) calculations predict the presence of an eight-fold degenerate band crossing whose topological properties are investigated in this thesis. The magnetoresistance in this material shows the onset of linear behaviour at 15 T which indicates the presence of Dirac-like band crossings, while the angular magnetoresistance (AMR) measurements also resemble results known from topological semimetals, however alternative explanations seem more likely to explain these results in NbTe₄. Experimental signatures expected from Dirac semimetals are further examined with a comprehensive study of the magnetic torque anomaly, and by measuring de Haas - van Alphen (dHvA) oscillations in the magnetic torque and Shubnikov - de Haas (SdH) oscillations in the magnetoresistance. Combined with DFT calculations, quantum oscillations allow to map the Fermi surface of this material. Furthermore, non-trivial Berry phases and low effective masses can be observed together with high frequencies that could either be the remains of a different CDW phase or arise from magnetic breakdown. Based on symmetry arguments of the crystal structure, the Dirac nodal-line semimetal candidate TaPtTe₅ is theoretically predicted to host four-fold degenerate lines with linear band dispersion in reciprocal space. The work presented here aims at confirming the theoretical predictions by providing a numerical investigation of the band structure and comparing that to results from dHvA oscillations in the magnetic torque. Closely related to TaPtTe₅, the structurally similar compound TaNiTe₅ is also predicted to host Dirac nodal-lines. Again, quantum oscillations in the magnetic torque are used to obtain insights into the morphology of the Fermi surface, while effective masses can be extracted from temperature-dependent dHvA measurements in the magnetisation. Unlike other semimetals reported in the literature, TaNiTe₅ furthermore shows enhanced oscillations in the magnetoresistance, even in the out-of-phase component of the applied alternating current. A thorough investigation of this effect is performed and a numerical model can explain the effect within the framework of classical electrodynamics without involvement of topological physics.","abstract_has_math":false,"creators":["Daschner, Maximilian"],"institution":"University of Cambridge","degree_name":null,"degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Grosche, Friedrich Malte"],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-09-28","date_published":"2024-09-28","updated_at":"2026-07-22T22:24:24Z","subjects":["quantum oscillations","Dirac semimetals"],"languages":["eng"],"rights":[],"rights_urls":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/c98bca97-0a03-4241-b24a-223abe3da7b5/download","http://purl.org/NET/rdflicense/allrightsreserved"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.118311","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Grosche, Friedrich Malte"]},{"key":"dc:creator","label":"Author","values":["Daschner, Maximilian"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2024-09-28"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/384254"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["quantum oscillations","Dirac semimetals"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/c98bca97-0a03-4241-b24a-223abe3da7b5/download","http://purl.org/NET/rdflicense/allrightsreserved"]},{"key":"dc:rights.embargotype","label":"Dc Rights Embargotype","values":["controlled.access"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["https://doi.org/10.17863/CAM.118311"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/8c8d1187-785d-4c93-a02c-a085a61bb863/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Dirac semimetals have recently gained interest due to their unique experimental signatures many of which can be explained by the topologically non-trivial band structure in these materials. 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The magnetoresistance in this material shows the onset of linear behaviour at 15 T which indicates the presence of Dirac-like band crossings, while the angular magnetoresistance (AMR) measurements also resemble results known from topological semimetals, however alternative explanations seem more likely to explain these results in NbTe₄. Experimental signatures expected from Dirac semimetals are further examined with a comprehensive study of the magnetic torque anomaly, and by measuring de Haas - van Alphen (dHvA) oscillations in the magnetic torque and Shubnikov - de Haas (SdH) oscillations in the magnetoresistance. Combined with DFT calculations, quantum oscillations allow to map the Fermi surface of this material. Furthermore, non-trivial Berry phases and low effective masses can be observed together with high frequencies that could either be the remains of a different CDW phase or arise from magnetic breakdown. Based on symmetry arguments of the crystal structure, the Dirac nodal-line semimetal candidate TaPtTe₅ is theoretically predicted to host four-fold degenerate lines with linear band dispersion in reciprocal space. The work presented here aims at confirming the theoretical predictions by providing a numerical investigation of the band structure and comparing that to results from dHvA oscillations in the magnetic torque. Closely related to TaPtTe₅, the structurally similar compound TaNiTe₅ is also predicted to host Dirac nodal-lines. Again, quantum oscillations in the magnetic torque are used to obtain insights into the morphology of the Fermi surface, while effective masses can be extracted from temperature-dependent dHvA measurements in the magnetisation. Unlike other semimetals reported in the literature, TaNiTe₅ furthermore shows enhanced oscillations in the magnetoresistance, even in the out-of-phase component of the applied alternating current. 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To probe their band structure and its corresponding Fermi surface, quantum oscillations have proven very useful as they provide a tool to directly measure the Berry phase under certain conditions. The (double) Dirac semimetal NbTe₄ has shown the occurrence of multiple charge-density-wave (CDW) phases, and as a result a complex band structure at low temperatures. Density functional theory (DFT) calculations predict the presence of an eight-fold degenerate band crossing whose topological properties are investigated in this thesis. The magnetoresistance in this material shows the onset of linear behaviour at 15 T which indicates the presence of Dirac-like band crossings, while the angular magnetoresistance (AMR) measurements also resemble results known from topological semimetals, however alternative explanations seem more likely to explain these results in NbTe₄. Experimental signatures expected from Dirac semimetals are further examined with a comprehensive study of the magnetic torque anomaly, and by measuring de Haas - van Alphen (dHvA) oscillations in the magnetic torque and Shubnikov - de Haas (SdH) oscillations in the magnetoresistance. Combined with DFT calculations, quantum oscillations allow to map the Fermi surface of this material. Furthermore, non-trivial Berry phases and low effective masses can be observed together with high frequencies that could either be the remains of a different CDW phase or arise from magnetic breakdown. Based on symmetry arguments of the crystal structure, the Dirac nodal-line semimetal candidate TaPtTe₅ is theoretically predicted to host four-fold degenerate lines with linear band dispersion in reciprocal space. The work presented here aims at confirming the theoretical predictions by providing a numerical investigation of the band structure and comparing that to results from dHvA oscillations in the magnetic torque. Closely related to TaPtTe₅, the structurally similar compound TaNiTe₅ is also predicted to host Dirac nodal-lines. Again, quantum oscillations in the magnetic torque are used to obtain insights into the morphology of the Fermi surface, while effective masses can be extracted from temperature-dependent dHvA measurements in the magnetisation. Unlike other semimetals reported in the literature, TaNiTe₅ furthermore shows enhanced oscillations in the magnetoresistance, even in the out-of-phase component of the applied alternating current. 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