{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/108119"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/108119","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Scanning tunneling microscopy studies of a tunable topological insulator and magnetic Weyl semimetal","abstract":"The discovery of topological order with material systems, and the unique electronic states necessitated by non-trivial topology, has been a major thrust of condensed matter research for the past two decades. As exotic topological electronic states often manifest themselves at reduced dimensional interfaces, local experimental probes play an important role in the understanding and development of topological materials. In this thesis, I describe the construction of a Scanning Tunneling Microscope (STM) for the study of topological materials. After construction, the tunable topological insulator system Ge(Bix,Sb1-x)2Te4 and the magnetic Weyl semimetal Co3Sn2S2 were studied. In Ge(Bix,Sb1-x)2Te4, increasing Sb substitution effectively electron dopes the sample and moves the Dirac point from 300 meV below the Fermi energy to energies above the Fermi energy while remaining topological. As the topological surface states in this material are well isolated from the bulk bands, Dirac point tuning in this material system has interesting consequences for potential spintronic applications, as well as existing thermoelectric and phase change applications. In Co3Sn2S2, the seminal model of a magnetic Weyl semimetal as a stacking of Chern insulators is extended to step edges exposed upon cleavage. We find that for a large region of parameter space within this model, the chiral edge states present in the 2D limit can be recovered on surfaces where the inter-layer coupling is sufficiently reduced. Our subsequent STM study finds an edge state on the kagome Co3Sn surface, which is predicted to be a Chern insulator in the 2D limit. STM density of states maps on thin terraces of the Co3Sn surface show quantum well like bound states that have a linear dependence on the nth bound state and energy. By constructing a tight binding model of linearly dispersing states that can hybridize, we reproduce our results on the terrace. These results suggest that elusive chiral edge states could be studied by local probe measurements within bulk materials. Additionally, our experiments provide evidence that Co3Sn2S2 could host the quantum anomalous Hall effect at elevated temperatures in the 2D limit.","abstract_html":"The discovery of topological order with material systems, and the unique electronic states necessitated by non-trivial topology, has been a major thrust of condensed matter research for the past two decades. As exotic topological electronic states often manifest themselves at reduced dimensional interfaces, local experimental probes play an important role in the understanding and development of topological materials. In this thesis, I describe the construction of a Scanning Tunneling Microscope (STM) for the study of topological materials. After construction, the tunable topological insulator system Ge(Bix,Sb1-x)2Te4 and the magnetic Weyl semimetal Co3Sn2S2 were studied. In Ge(Bix,Sb1-x)2Te4, increasing Sb substitution effectively electron dopes the sample and moves the Dirac point from 300 meV below the Fermi energy to energies above the Fermi energy while remaining topological. As the topological surface states in this material are well isolated from the bulk bands, Dirac point tuning in this material system has interesting consequences for potential spintronic applications, as well as existing thermoelectric and phase change applications. In Co3Sn2S2, the seminal model of a magnetic Weyl semimetal as a stacking of Chern insulators is extended to step edges exposed upon cleavage. We find that for a large region of parameter space within this model, the chiral edge states present in the 2D limit can be recovered on surfaces where the inter-layer coupling is sufficiently reduced. Our subsequent STM study finds an edge state on the kagome Co3Sn surface, which is predicted to be a Chern insulator in the 2D limit. STM density of states maps on thin terraces of the Co3Sn surface show quantum well like bound states that have a linear dependence on the nth bound state and energy. By constructing a tight binding model of linearly dispersing states that can hybridize, we reproduce our results on the terrace. These results suggest that elusive chiral edge states could be studied by local probe measurements within bulk materials. Additionally, our experiments provide evidence that Co3Sn2S2 could host the quantum anomalous Hall effect at elevated temperatures in the 2D limit.","abstract_has_math":false,"creators":["Howard, Sean T"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Madhavan, Vidya","Mahmood, Fahad","Hughes, Taylor","Gadway, Bryce"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2020,"date_issued":"2020-08-26T23:54:36Z","date_published":"2020-08-26T23:54:36Z","updated_at":"2026-07-22T22:24:47Z","subjects":["Scanning Tunneling Microscopy","Topological Insulator","Weyl Semimetal"],"languages":["en"],"rights":["Copyright 2020 Sean Howard"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/108119","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Madhavan, Vidya","Mahmood, Fahad","Hughes, Taylor","Gadway, Bryce"]},{"key":"dc:creator","label":"Author","values":["Howard, Sean T"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2020-08-26T23:54:36Z","2022-08-26T23:58:55Z","2020-04-22","2020-05"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Scanning Tunneling Microscopy","Topological Insulator","Weyl Semimetal"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2020 Sean Howard"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/108119"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["The discovery of topological order with material systems, and the unique electronic states necessitated by non-trivial topology, has been a major thrust of condensed matter research for the past two decades. As exotic topological electronic states often manifest themselves at reduced dimensional interfaces, local experimental probes play an important role in the understanding and development of topological materials. In this thesis, I describe the construction of a Scanning Tunneling Microscope (STM) for the study of topological materials. After construction, the tunable topological insulator system Ge(Bix,Sb1-x)2Te4 and the magnetic Weyl semimetal Co3Sn2S2 were studied. In Ge(Bix,Sb1-x)2Te4, increasing Sb substitution effectively electron dopes the sample and moves the Dirac point from 300 meV below the Fermi energy to energies above the Fermi energy while remaining topological. As the topological surface states in this material are well isolated from the bulk bands, Dirac point tuning in this material system has interesting consequences for potential spintronic applications, as well as existing thermoelectric and phase change applications. In Co3Sn2S2, the seminal model of a magnetic Weyl semimetal as a stacking of Chern insulators is extended to step edges exposed upon cleavage. We find that for a large region of parameter space within this model, the chiral edge states present in the 2D limit can be recovered on surfaces where the inter-layer coupling is sufficiently reduced. Our subsequent STM study finds an edge state on the kagome Co3Sn surface, which is predicted to be a Chern insulator in the 2D limit. STM density of states maps on thin terraces of the Co3Sn surface show quantum well like bound states that have a linear dependence on the nth bound state and energy. By constructing a tight binding model of linearly dispersing states that can hybridize, we reproduce our results on the terrace. These results suggest that elusive chiral edge states could be studied by local probe measurements within bulk materials. Additionally, our experiments provide evidence that Co3Sn2S2 could host the quantum anomalous Hall effect at elevated temperatures in the 2D limit.","Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2022-05-01","The student, Sean Howard, accepted the attached license on 2020-04-22 at 10:07.","The student, Sean Howard, submitted this Dissertation for approval on 2020-04-22 at 10:16.","This Dissertation was approved for publication on 2020-04-22 at 15:59.","DSpace SAF Submission Ingestion Package generated from Vireo submission #15032 on 2020-08-25 at 17:27:57","Made available in DSpace on 2020-08-26T23:54:36Z (GMT). No. of bitstreams: 2 HOWARD-DISSERTATION-2020.pdf: 22327326 bytes, checksum: b9fcb9c6fe1618d078deac006a87d160 (MD5) LICENSE.txt: 4208 bytes, checksum: 1f72b641d6c35dfa5f8b2c10ba6ca5a5 (MD5) Previous issue date: 2020-04-22","Embargo set by: Seth Robbins for item 115729 Lift date: 2022-08-26T23:54:40Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Embargo set by: Seth Robbins for item 115729 Lift date: 2022-08-26T23:55:59Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Embargo set by: Seth Robbins for item 115729 Lift date: 2022-08-26T23:57:28Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Embargo set by: Seth Robbins for item 115729 Lift date: 2022-08-26T23:58:55Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","U of I Only"]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Scanning tunneling microscopy studies of a tunable topological insulator and magnetic Weyl semimetal"]}]}],"canonical_facts":{"dc:contributor":["Madhavan, Vidya","Mahmood, Fahad","Hughes, Taylor","Gadway, Bryce"],"dc:creator":["Howard, Sean T"],"dc:date":["2020-08-26T23:54:36Z","2022-08-26T23:58:55Z","2020-04-22","2020-05"],"dc:description":["The discovery of topological order with material systems, and the unique electronic states necessitated by non-trivial topology, has been a major thrust of condensed matter research for the past two decades. As exotic topological electronic states often manifest themselves at reduced dimensional interfaces, local experimental probes play an important role in the understanding and development of topological materials. In this thesis, I describe the construction of a Scanning Tunneling Microscope (STM) for the study of topological materials. After construction, the tunable topological insulator system Ge(Bix,Sb1-x)2Te4 and the magnetic Weyl semimetal Co3Sn2S2 were studied. In Ge(Bix,Sb1-x)2Te4, increasing Sb substitution effectively electron dopes the sample and moves the Dirac point from 300 meV below the Fermi energy to energies above the Fermi energy while remaining topological. As the topological surface states in this material are well isolated from the bulk bands, Dirac point tuning in this material system has interesting consequences for potential spintronic applications, as well as existing thermoelectric and phase change applications. In Co3Sn2S2, the seminal model of a magnetic Weyl semimetal as a stacking of Chern insulators is extended to step edges exposed upon cleavage. We find that for a large region of parameter space within this model, the chiral edge states present in the 2D limit can be recovered on surfaces where the inter-layer coupling is sufficiently reduced. Our subsequent STM study finds an edge state on the kagome Co3Sn surface, which is predicted to be a Chern insulator in the 2D limit. STM density of states maps on thin terraces of the Co3Sn surface show quantum well like bound states that have a linear dependence on the nth bound state and energy. By constructing a tight binding model of linearly dispersing states that can hybridize, we reproduce our results on the terrace. These results suggest that elusive chiral edge states could be studied by local probe measurements within bulk materials. Additionally, our experiments provide evidence that Co3Sn2S2 could host the quantum anomalous Hall effect at elevated temperatures in the 2D limit.","Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2022-05-01","The student, Sean Howard, accepted the attached license on 2020-04-22 at 10:07.","The student, Sean Howard, submitted this Dissertation for approval on 2020-04-22 at 10:16.","This Dissertation was approved for publication on 2020-04-22 at 15:59.","DSpace SAF Submission Ingestion Package generated from Vireo submission #15032 on 2020-08-25 at 17:27:57","Made available in DSpace on 2020-08-26T23:54:36Z (GMT). No. of bitstreams: 2 HOWARD-DISSERTATION-2020.pdf: 22327326 bytes, checksum: b9fcb9c6fe1618d078deac006a87d160 (MD5) LICENSE.txt: 4208 bytes, checksum: 1f72b641d6c35dfa5f8b2c10ba6ca5a5 (MD5) Previous issue date: 2020-04-22","Embargo set by: Seth Robbins for item 115729 Lift date: 2022-08-26T23:54:40Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Embargo set by: Seth Robbins for item 115729 Lift date: 2022-08-26T23:55:59Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Embargo set by: Seth Robbins for item 115729 Lift date: 2022-08-26T23:57:28Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Embargo set by: Seth Robbins for item 115729 Lift date: 2022-08-26T23:58:55Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","U of I Only"],"dc:format":["application/pdf"],"dc:identifier":["http://hdl.handle.net/2142/108119"],"dc:language":["en"],"dc:rights":["Copyright 2020 Sean Howard"],"dc:subject":["Scanning Tunneling Microscopy","Topological Insulator","Weyl Semimetal"],"dc:title":["Scanning tunneling microscopy studies of a tunable topological insulator and magnetic Weyl semimetal"],"dc:type":["text","Thesis"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:24:47Z"}