{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/108226"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/108226","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Angle-resolved photoemission studies of topological thin films and superconducting heterostructures","abstract":"In recent years, topological phases of matter have remained at the forefront of condensed-matter physics research due to the presence of unusually robust, conducting boundary states in these systems. Their unique bulk electronic band structures in tandem with these topologically protected states allows these materials to potentially display many fascinating physical properties, including the quantum anomalous Hall effect, emergent phenomena such as Majorana fermions, supersymmetry, and skyrmions, and unconventional superconductivity. Many of these materials are thus highly suitable for applications in spintronics and fault-tolerant quantum computing. During this thesis research, high-quality, single-crystalline ultrathin topological films and heterostructures are prepared using a combination of molecular beam epitaxy (MBE), DC magnetron sputtering, and ex situ sample-cleavage preparation techniques. Films grown using MBE are characterized in situ during the growths using electron diffraction techniques, such as reflection high-energy electron diffraction (RHEED). Angle-resolved photoemission spectroscopy (ARPES) is employed to quantify the electronic band structure of all topological films and associated heterostructures. Systems fabricated during this dissertation research include the topological insulators (TIs) Bi2Te3 and Bi2Se3, the TI/superconductor (SC) heterostructure (Bi{1-x}Sbx)2Te3/Nb, and the Type-II Dirac semimetal candidate NiTe2. A major component of this thesis research was the engineering of clean, nearly intrinsic TI/SC systems to probe the mechanism of proximity-induced pairing in these systems. Interfacing a TI with a simple isotropic s-wave superconductor may initiate exotic p-wave-like pairing in the topological surface states (TSSs). Realizing this unconventional superconductivity is dependent on the quantum-mechanical coupling between the bulk and topological surface states; however, the underlying physics is still under debate. By using a cleavage-based flip-chip approach, we have fabricated single-crystalline, bulk insulating (Bi{1-x}Sbx)2Te3 films (of thicknesses N = 2 – 10 layers) each of a predetermined layer thickness and with a strategically chosen composition ratio x = 0.62 on superconducting Nb films. Our ARPES characterizations demonstrate that each film prepared on Nb is slightly n-doped and bulk insulating by design, in both the bulk and ultrathin-film limits. Using ultrahigh-resolution laser-ARPES, proximity-induced superconducting gaps in the (Bi{1-x}Sbx)2Te3/Nb system are measured as a function of TI film thickness and temperature; these results are then compared with corresponding results from our prior studies on heavily n-doped TI films (with bulk carriers). We discover that superconductivity is greatly suppressed in slightly n-doped, bulk insulating (Bi{1-x}Sbx)2Te3/Nb, suggesting that bulk carriers are required for transiting superconductivity from the superconducting substrate to the surface of a TI film. Lastly, the other component of this thesis research focused on the fabrication and characterization of newly proposed topological systems. To that end, high-quality, single-crystalline thin films of the Type-II topological Dirac semimetal (TDS) candidate NiTe2 are grown on bilayer-graphene-terminated 6H-SiC(0001) (BLG/SiC). Our ARPES results demonstrate that this Dirac semimetal candidate is a semimetal with a complex Fermi surface in the thin-film limit. Thickness-dependent evolution of the electronic band structure is also evident in the ARPES spectra presented herein, though the band structure of the thinnest films is complicated due to their tendency to form multilayer films in the ultrathin-film regime. Consistent with prior studies, we confirm that the bulk Type-II Dirac point of NiTe2 apparently lies very near and above the Fermi level, quite unlike other Type-II Dirac semimetal systems such as PtTe2 and PdTe2; this suggests that creating alloy systems such as Pt{1-x}NixTe2 may likely be an efficient means for tuning the binding energy position of the bulk Type-II Dirac point relative to the Fermi level and thus the underlying transport properties.","abstract_html":"In recent years, topological phases of matter have remained at the forefront of condensed-matter physics research due to the presence of unusually robust, conducting boundary states in these systems. Their unique bulk electronic band structures in tandem with these topologically protected states allows these materials to potentially display many fascinating physical properties, including the quantum anomalous Hall effect, emergent phenomena such as Majorana fermions, supersymmetry, and skyrmions, and unconventional superconductivity. Many of these materials are thus highly suitable for applications in spintronics and fault-tolerant quantum computing. During this thesis research, high-quality, single-crystalline ultrathin topological films and heterostructures are prepared using a combination of molecular beam epitaxy (MBE), DC magnetron sputtering, and ex situ sample-cleavage preparation techniques. Films grown using MBE are characterized in situ during the growths using electron diffraction techniques, such as reflection high-energy electron diffraction (RHEED). Angle-resolved photoemission spectroscopy (ARPES) is employed to quantify the electronic band structure of all topological films and associated heterostructures. Systems fabricated during this dissertation research include the topological insulators (TIs) Bi2Te3 and Bi2Se3, the TI/superconductor (SC) heterostructure (Bi{1-x}Sbx)2Te3/Nb, and the Type-II Dirac semimetal candidate NiTe2. A major component of this thesis research was the engineering of clean, nearly intrinsic TI/SC systems to probe the mechanism of proximity-induced pairing in these systems. Interfacing a TI with a simple isotropic s-wave superconductor may initiate exotic p-wave-like pairing in the topological surface states (TSSs). Realizing this unconventional superconductivity is dependent on the quantum-mechanical coupling between the bulk and topological surface states; however, the underlying physics is still under debate. By using a cleavage-based flip-chip approach, we have fabricated single-crystalline, bulk insulating (Bi{1-x}Sbx)2Te3 films (of thicknesses N = 2 – 10 layers) each of a predetermined layer thickness and with a strategically chosen composition ratio x = 0.62 on superconducting Nb films. Our ARPES characterizations demonstrate that each film prepared on Nb is slightly n-doped and bulk insulating by design, in both the bulk and ultrathin-film limits. Using ultrahigh-resolution laser-ARPES, proximity-induced superconducting gaps in the (Bi{1-x}Sbx)2Te3/Nb system are measured as a function of TI film thickness and temperature; these results are then compared with corresponding results from our prior studies on heavily n-doped TI films (with bulk carriers). We discover that superconductivity is greatly suppressed in slightly n-doped, bulk insulating (Bi{1-x}Sbx)2Te3/Nb, suggesting that bulk carriers are required for transiting superconductivity from the superconducting substrate to the surface of a TI film. Lastly, the other component of this thesis research focused on the fabrication and characterization of newly proposed topological systems. To that end, high-quality, single-crystalline thin films of the Type-II topological Dirac semimetal (TDS) candidate NiTe2 are grown on bilayer-graphene-terminated 6H-SiC(0001) (BLG/SiC). Our ARPES results demonstrate that this Dirac semimetal candidate is a semimetal with a complex Fermi surface in the thin-film limit. Thickness-dependent evolution of the electronic band structure is also evident in the ARPES spectra presented herein, though the band structure of the thinnest films is complicated due to their tendency to form multilayer films in the ultrathin-film regime. Consistent with prior studies, we confirm that the bulk Type-II Dirac point of NiTe2 apparently lies very near and above the Fermi level, quite unlike other Type-II Dirac semimetal systems such as PtTe2 and PdTe2; this suggests that creating alloy systems such as Pt{1-x}NixTe2 may likely be an efficient means for tuning the binding energy position of the bulk Type-II Dirac point relative to the Fermi level and thus the underlying transport properties.","abstract_has_math":false,"creators":["Hlevyack, Joseph Andrew"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Chiang, Tai-Chang","Madhavan, Vidya","Stone, Michael","Stack, John"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2020,"date_issued":"2020-08-27T00:46:51Z","date_published":"2020-08-27T00:46:51Z","updated_at":"2026-07-22T22:24:48Z","subjects":["Angle-resolved photoemission spectroscopy (ARPES), Topological insulators, Topological superconductivity, Proximity pairing, Topological Dirac semimetals, Molecular beam epitaxy (MBE), Thin films"],"languages":["en"],"rights":["Copyright 2020 J. A. Hlevyack"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/108226","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Chiang, Tai-Chang","Madhavan, Vidya","Stone, Michael","Stack, John"]},{"key":"dc:creator","label":"Author","values":["Hlevyack, Joseph Andrew"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2020-08-27T00:46:51Z","2022-08-27T00:51:40Z","2020-03-02","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":["Angle-resolved photoemission spectroscopy (ARPES), Topological insulators, Topological superconductivity, Proximity pairing, Topological Dirac semimetals, Molecular beam epitaxy (MBE), Thin films"]}]},{"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 J. A. Hlevyack"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/108226"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["In recent years, topological phases of matter have remained at the forefront of condensed-matter physics research due to the presence of unusually robust, conducting boundary states in these systems. Their unique bulk electronic band structures in tandem with these topologically protected states allows these materials to potentially display many fascinating physical properties, including the quantum anomalous Hall effect, emergent phenomena such as Majorana fermions, supersymmetry, and skyrmions, and unconventional superconductivity. Many of these materials are thus highly suitable for applications in spintronics and fault-tolerant quantum computing. During this thesis research, high-quality, single-crystalline ultrathin topological films and heterostructures are prepared using a combination of molecular beam epitaxy (MBE), DC magnetron sputtering, and ex situ sample-cleavage preparation techniques. Films grown using MBE are characterized in situ during the growths using electron diffraction techniques, such as reflection high-energy electron diffraction (RHEED). Angle-resolved photoemission spectroscopy (ARPES) is employed to quantify the electronic band structure of all topological films and associated heterostructures. Systems fabricated during this dissertation research include the topological insulators (TIs) Bi2Te3 and Bi2Se3, the TI/superconductor (SC) heterostructure (Bi{1-x}Sbx)2Te3/Nb, and the Type-II Dirac semimetal candidate NiTe2. A major component of this thesis research was the engineering of clean, nearly intrinsic TI/SC systems to probe the mechanism of proximity-induced pairing in these systems. Interfacing a TI with a simple isotropic s-wave superconductor may initiate exotic p-wave-like pairing in the topological surface states (TSSs). Realizing this unconventional superconductivity is dependent on the quantum-mechanical coupling between the bulk and topological surface states; however, the underlying physics is still under debate. By using a cleavage-based flip-chip approach, we have fabricated single-crystalline, bulk insulating (Bi{1-x}Sbx)2Te3 films (of thicknesses N = 2 – 10 layers) each of a predetermined layer thickness and with a strategically chosen composition ratio x = 0.62 on superconducting Nb films. Our ARPES characterizations demonstrate that each film prepared on Nb is slightly n-doped and bulk insulating by design, in both the bulk and ultrathin-film limits. Using ultrahigh-resolution laser-ARPES, proximity-induced superconducting gaps in the (Bi{1-x}Sbx)2Te3/Nb system are measured as a function of TI film thickness and temperature; these results are then compared with corresponding results from our prior studies on heavily n-doped TI films (with bulk carriers). We discover that superconductivity is greatly suppressed in slightly n-doped, bulk insulating (Bi{1-x}Sbx)2Te3/Nb, suggesting that bulk carriers are required for transiting superconductivity from the superconducting substrate to the surface of a TI film. Lastly, the other component of this thesis research focused on the fabrication and characterization of newly proposed topological systems. To that end, high-quality, single-crystalline thin films of the Type-II topological Dirac semimetal (TDS) candidate NiTe2 are grown on bilayer-graphene-terminated 6H-SiC(0001) (BLG/SiC). Our ARPES results demonstrate that this Dirac semimetal candidate is a semimetal with a complex Fermi surface in the thin-film limit. Thickness-dependent evolution of the electronic band structure is also evident in the ARPES spectra presented herein, though the band structure of the thinnest films is complicated due to their tendency to form multilayer films in the ultrathin-film regime. Consistent with prior studies, we confirm that the bulk Type-II Dirac point of NiTe2 apparently lies very near and above the Fermi level, quite unlike other Type-II Dirac semimetal systems such as PtTe2 and PdTe2; this suggests that creating alloy systems such as Pt{1-x}NixTe2 may likely be an efficient means for tuning the binding energy position of the bulk Type-II Dirac point relative to the Fermi level and thus the underlying transport properties.","Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2022-05-01","The student, Joseph Hlevyack, accepted the attached license on 2020-02-28 at 10:54.","The student, Joseph Hlevyack, submitted this Dissertation for approval on 2020-02-28 at 12:25.","This Dissertation was approved for publication on 2020-03-02 at 11:05.","DSpace SAF Submission Ingestion Package generated from Vireo submission #14881 on 2020-08-25 at 17:38:52","Made available in DSpace on 2020-08-27T00:46:51Z (GMT). No. of bitstreams: 2 HLEVYACK-DISSERTATION-2020.pdf: 21552914 bytes, checksum: 7fcca5d293f934c7c9580d09e373bf87 (MD5) LICENSE.txt: 4212 bytes, checksum: d66b87a8a49181aab1a46d30141e9d03 (MD5) Previous issue date: 2020-03-02","Embargo set by: Seth Robbins for item 115839 Lift date: 2022-08-27T00:46:59Z Reason: Author requested closed access (OA after 2yrs) in Vireo ETD system","Embargo set by: Seth Robbins for item 115839 Lift date: 2022-08-27T00:50:22Z Reason: Author requested closed access (OA after 2yrs) in Vireo ETD system","Embargo set by: Seth Robbins for item 115839 Lift date: 2022-08-27T00:51:40Z Reason: Author requested closed access (OA after 2yrs) in Vireo ETD system","Author requested closed access (OA after 2yrs) in Vireo ETD system","Limited"]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Angle-resolved photoemission studies of topological thin films and superconducting heterostructures"]}]}],"canonical_facts":{"dc:contributor":["Chiang, Tai-Chang","Madhavan, Vidya","Stone, Michael","Stack, John"],"dc:creator":["Hlevyack, Joseph Andrew"],"dc:date":["2020-08-27T00:46:51Z","2022-08-27T00:51:40Z","2020-03-02","2020-05"],"dc:description":["In recent years, topological phases of matter have remained at the forefront of condensed-matter physics research due to the presence of unusually robust, conducting boundary states in these systems. Their unique bulk electronic band structures in tandem with these topologically protected states allows these materials to potentially display many fascinating physical properties, including the quantum anomalous Hall effect, emergent phenomena such as Majorana fermions, supersymmetry, and skyrmions, and unconventional superconductivity. Many of these materials are thus highly suitable for applications in spintronics and fault-tolerant quantum computing. During this thesis research, high-quality, single-crystalline ultrathin topological films and heterostructures are prepared using a combination of molecular beam epitaxy (MBE), DC magnetron sputtering, and ex situ sample-cleavage preparation techniques. Films grown using MBE are characterized in situ during the growths using electron diffraction techniques, such as reflection high-energy electron diffraction (RHEED). Angle-resolved photoemission spectroscopy (ARPES) is employed to quantify the electronic band structure of all topological films and associated heterostructures. Systems fabricated during this dissertation research include the topological insulators (TIs) Bi2Te3 and Bi2Se3, the TI/superconductor (SC) heterostructure (Bi{1-x}Sbx)2Te3/Nb, and the Type-II Dirac semimetal candidate NiTe2. A major component of this thesis research was the engineering of clean, nearly intrinsic TI/SC systems to probe the mechanism of proximity-induced pairing in these systems. Interfacing a TI with a simple isotropic s-wave superconductor may initiate exotic p-wave-like pairing in the topological surface states (TSSs). Realizing this unconventional superconductivity is dependent on the quantum-mechanical coupling between the bulk and topological surface states; however, the underlying physics is still under debate. By using a cleavage-based flip-chip approach, we have fabricated single-crystalline, bulk insulating (Bi{1-x}Sbx)2Te3 films (of thicknesses N = 2 – 10 layers) each of a predetermined layer thickness and with a strategically chosen composition ratio x = 0.62 on superconducting Nb films. Our ARPES characterizations demonstrate that each film prepared on Nb is slightly n-doped and bulk insulating by design, in both the bulk and ultrathin-film limits. Using ultrahigh-resolution laser-ARPES, proximity-induced superconducting gaps in the (Bi{1-x}Sbx)2Te3/Nb system are measured as a function of TI film thickness and temperature; these results are then compared with corresponding results from our prior studies on heavily n-doped TI films (with bulk carriers). We discover that superconductivity is greatly suppressed in slightly n-doped, bulk insulating (Bi{1-x}Sbx)2Te3/Nb, suggesting that bulk carriers are required for transiting superconductivity from the superconducting substrate to the surface of a TI film. Lastly, the other component of this thesis research focused on the fabrication and characterization of newly proposed topological systems. To that end, high-quality, single-crystalline thin films of the Type-II topological Dirac semimetal (TDS) candidate NiTe2 are grown on bilayer-graphene-terminated 6H-SiC(0001) (BLG/SiC). Our ARPES results demonstrate that this Dirac semimetal candidate is a semimetal with a complex Fermi surface in the thin-film limit. Thickness-dependent evolution of the electronic band structure is also evident in the ARPES spectra presented herein, though the band structure of the thinnest films is complicated due to their tendency to form multilayer films in the ultrathin-film regime. Consistent with prior studies, we confirm that the bulk Type-II Dirac point of NiTe2 apparently lies very near and above the Fermi level, quite unlike other Type-II Dirac semimetal systems such as PtTe2 and PdTe2; this suggests that creating alloy systems such as Pt{1-x}NixTe2 may likely be an efficient means for tuning the binding energy position of the bulk Type-II Dirac point relative to the Fermi level and thus the underlying transport properties.","Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2022-05-01","The student, Joseph Hlevyack, accepted the attached license on 2020-02-28 at 10:54.","The student, Joseph Hlevyack, submitted this Dissertation for approval on 2020-02-28 at 12:25.","This Dissertation was approved for publication on 2020-03-02 at 11:05.","DSpace SAF Submission Ingestion Package generated from Vireo submission #14881 on 2020-08-25 at 17:38:52","Made available in DSpace on 2020-08-27T00:46:51Z (GMT). No. of bitstreams: 2 HLEVYACK-DISSERTATION-2020.pdf: 21552914 bytes, checksum: 7fcca5d293f934c7c9580d09e373bf87 (MD5) LICENSE.txt: 4212 bytes, checksum: d66b87a8a49181aab1a46d30141e9d03 (MD5) Previous issue date: 2020-03-02","Embargo set by: Seth Robbins for item 115839 Lift date: 2022-08-27T00:46:59Z Reason: Author requested closed access (OA after 2yrs) in Vireo ETD system","Embargo set by: Seth Robbins for item 115839 Lift date: 2022-08-27T00:50:22Z Reason: Author requested closed access (OA after 2yrs) in Vireo ETD system","Embargo set by: Seth Robbins for item 115839 Lift date: 2022-08-27T00:51:40Z Reason: Author requested closed access (OA after 2yrs) in Vireo ETD system","Author requested closed access (OA after 2yrs) in Vireo ETD system","Limited"],"dc:format":["application/pdf"],"dc:identifier":["http://hdl.handle.net/2142/108226"],"dc:language":["en"],"dc:rights":["Copyright 2020 J. A. Hlevyack"],"dc:subject":["Angle-resolved photoemission spectroscopy (ARPES), Topological insulators, Topological superconductivity, Proximity pairing, Topological Dirac semimetals, Molecular beam epitaxy (MBE), Thin films"],"dc:title":["Angle-resolved photoemission studies of topological thin films and superconducting heterostructures"],"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":"2026-07-22T22:24:48Z"}