{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/301509"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/301509","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Quantum transport in gapped graphene","abstract":"This thesis focuses on investigating local and nonlocal transport properties in hexagonal boron nitride (hBN)/graphene superlattice Hall bars and graphene Hall bars proximity coupled to the ferrimagnetic insulator yttrium iron garnet ($\\text{Y}_{3}\\text{Fe}_{5}\\text{O}_{12}$ or YIG). The first part describes in detail the pulse laser deposition of atomically flat YIG thin films onto single crystal gadolinium gallium garnet with a magnetization of 144 emu cm$^{-3}$. This part also outlines device fabrication procedures including graphene exfoliation and dry transfer, electron beam lithography and metallization of side-contacts, and finally the electrical setup for measuring local and nonlocal transport in graphene. The second part investigates transport properties in hBN/graphene/hBN superlattice Hall bars with a field-effect mobility of up to 220,000 cm$^{2}$ V$^{-1}$ s$^{-1}$ at 9 K with low charge impurities. By aligning hBN and graphene, a ∼33.7 meV band gap at 9 K is demonstrated at the primary Dirac point in zero magnetic field. Furthermore, the nonlocal resistances approach $h/2e^{2}$, where $h$ is Planck’s constant and e is the electron charge. Nonlocal measurements demonstrate that, below 60 K a spin-degenerate ballistic counter-propagating edge state forms and dominates with a possible secondary contribution from a network of one-dimensional conducting channels with soliton-like domain walls. The spin-degenerate ballistic edge states offer possibilities for electronic applications beyond quantum spin and anomalous Hall effects since a quantized resistance is observed through valley coupling. The third part reports a proximity-induced magnetic exchange field in graphene of the order 60 T by placing graphene on the ferrimagnetic insulator YIG. From electrical transport measurements, the magnetic order and energy gap of the edge modes in graphene are tunable, and a transition between the canted antiferromagnetic and spin-polarized ferromagnetic $ν = 0$ quantum Hall states can be achieved with relatively low magnetic fields ($> 6$ T) at 2.7 K. The fourth part summarizes the key results of the thesis.","abstract_html":"This thesis focuses on investigating local and nonlocal transport properties in hexagonal boron nitride (hBN)/graphene superlattice Hall bars and graphene Hall bars proximity coupled to the ferrimagnetic insulator yttrium iron garnet (<span class=\"etd-inline-math\">\\text{Y}<sub>3</sub>\\text{Fe}<sub>5</sub>\\text{O}<sub>12</sub></span> or YIG). The first part describes in detail the pulse laser deposition of atomically flat YIG thin films onto single crystal gadolinium gallium garnet with a magnetization of 144 emu cm<span class=\"etd-inline-math\"><sup>-3</sup></span>. This part also outlines device fabrication procedures including graphene exfoliation and dry transfer, electron beam lithography and metallization of side-contacts, and finally the electrical setup for measuring local and nonlocal transport in graphene. The second part investigates transport properties in hBN/graphene/hBN superlattice Hall bars with a field-effect mobility of up to 220,000 cm<span class=\"etd-inline-math\"><sup>2</sup></span> V<span class=\"etd-inline-math\"><sup>-1</sup></span> s<span class=\"etd-inline-math\"><sup>-1</sup></span> at 9 K with low charge impurities. By aligning hBN and graphene, a ∼33.7 meV band gap at 9 K is demonstrated at the primary Dirac point in zero magnetic field. Furthermore, the nonlocal resistances approach <span class=\"etd-inline-math\">h/2e<sup>2</sup></span>, where $h$ is Planck’s constant and e is the electron charge. Nonlocal measurements demonstrate that, below 60 K a spin-degenerate ballistic counter-propagating edge state forms and dominates with a possible secondary contribution from a network of one-dimensional conducting channels with soliton-like domain walls. The spin-degenerate ballistic edge states offer possibilities for electronic applications beyond quantum spin and anomalous Hall effects since a quantized resistance is observed through valley coupling. The third part reports a proximity-induced magnetic exchange field in graphene of the order 60 T by placing graphene on the ferrimagnetic insulator YIG. From electrical transport measurements, the magnetic order and energy gap of the edge modes in graphene are tunable, and a transition between the canted antiferromagnetic and spin-polarized ferromagnetic $ν = 0$ quantum Hall states can be achieved with relatively low magnetic fields ($&gt; 6$ T) at 2.7 K. The fourth part summarizes the key results of the thesis.","abstract_has_math":true,"creators":["Li, Yang"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Robinson, Jason"],"committee_chairs":[],"committee_members":[],"year":2020,"date_issued":"2020-05-16","date_published":"2020-05-16","updated_at":"2026-07-24T01:33:03Z","subjects":["Graphene","Quantum effect","Edge state","Nonlocal transport","Proximity effect"],"languages":["en"],"rights":[],"rights_urls":["https://www.repository.cam.ac.uk/bitstreams/837f6e32-e5bd-4b6b-81fc-011301190621/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.48578","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Robinson, Jason"]},{"key":"dc:contributor.sponsor","label":"Sponsor","values":["Cambridge Trust and China Scholarship Committee"]},{"key":"dc:creator","label":"Author","values":["Li, Yang"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2020-05-16"]},{"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/1810/301509"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Graphene","Quantum effect","Edge state","Nonlocal transport","Proximity effect"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["https://www.repository.cam.ac.uk/bitstreams/837f6e32-e5bd-4b6b-81fc-011301190621/download","https://www.rioxx.net/licenses/all-rights-reserved/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["10.17863/CAM.48578"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://www.repository.cam.ac.uk/bitstreams/a0675f87-06ca-4b0e-a580-28862a68cb20/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["This thesis focuses on investigating local and nonlocal transport properties in hexagonal boron nitride (hBN)/graphene superlattice Hall bars and graphene Hall bars proximity coupled to the ferrimagnetic insulator yttrium iron garnet ($\\text{Y}_{3}\\text{Fe}_{5}\\text{O}_{12}$ or YIG). The first part describes in detail the pulse laser deposition of atomically flat YIG thin films onto single crystal gadolinium gallium garnet with a magnetization of 144 emu cm$^{-3}$. This part also outlines device fabrication procedures including graphene exfoliation and dry transfer, electron beam lithography and metallization of side-contacts, and finally the electrical setup for measuring local and nonlocal transport in graphene. The second part investigates transport properties in hBN/graphene/hBN superlattice Hall bars with a field-effect mobility of up to 220,000 cm$^{2}$ V$^{-1}$ s$^{-1}$ at 9 K with low charge impurities. By aligning hBN and graphene, a ∼33.7 meV band gap at 9 K is demonstrated at the primary Dirac point in zero magnetic field. Furthermore, the nonlocal resistances approach $h/2e^{2}$, where $h$ is Planck’s constant and e is the electron charge. Nonlocal measurements demonstrate that, below 60 K a spin-degenerate ballistic counter-propagating edge state forms and dominates with a possible secondary contribution from a network of one-dimensional conducting channels with soliton-like domain walls. The spin-degenerate ballistic edge states offer possibilities for electronic applications beyond quantum spin and anomalous Hall effects since a quantized resistance is observed through valley coupling. The third part reports a proximity-induced magnetic exchange field in graphene of the order 60 T by placing graphene on the ferrimagnetic insulator YIG. From electrical transport measurements, the magnetic order and energy gap of the edge modes in graphene are tunable, and a transition between the canted antiferromagnetic and spin-polarized ferromagnetic $ν = 0$ quantum Hall states can be achieved with relatively low magnetic fields ($> 6$ T) at 2.7 K. The fourth part summarizes the key results of the thesis."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["2597238f74d2682e0d12b1074eaa4dba","87eda9de84448d1f82354d60eee3eb5f"]},{"key":"dc:title","label":"Title","values":["Quantum transport in gapped graphene"]}]}],"canonical_facts":{"dc:contributor.advisor":["Robinson, Jason"],"dc:contributor.sponsor":["Cambridge Trust and China Scholarship Committee"],"dc:creator":["Li, Yang"],"dc:date.issued":["2020-05-16"],"dc:description.abstract":["This thesis focuses on investigating local and nonlocal transport properties in hexagonal boron nitride (hBN)/graphene superlattice Hall bars and graphene Hall bars proximity coupled to the ferrimagnetic insulator yttrium iron garnet ($\\text{Y}_{3}\\text{Fe}_{5}\\text{O}_{12}$ or YIG). The first part describes in detail the pulse laser deposition of atomically flat YIG thin films onto single crystal gadolinium gallium garnet with a magnetization of 144 emu cm$^{-3}$. This part also outlines device fabrication procedures including graphene exfoliation and dry transfer, electron beam lithography and metallization of side-contacts, and finally the electrical setup for measuring local and nonlocal transport in graphene. The second part investigates transport properties in hBN/graphene/hBN superlattice Hall bars with a field-effect mobility of up to 220,000 cm$^{2}$ V$^{-1}$ s$^{-1}$ at 9 K with low charge impurities. By aligning hBN and graphene, a ∼33.7 meV band gap at 9 K is demonstrated at the primary Dirac point in zero magnetic field. Furthermore, the nonlocal resistances approach $h/2e^{2}$, where $h$ is Planck’s constant and e is the electron charge. Nonlocal measurements demonstrate that, below 60 K a spin-degenerate ballistic counter-propagating edge state forms and dominates with a possible secondary contribution from a network of one-dimensional conducting channels with soliton-like domain walls. The spin-degenerate ballistic edge states offer possibilities for electronic applications beyond quantum spin and anomalous Hall effects since a quantized resistance is observed through valley coupling. The third part reports a proximity-induced magnetic exchange field in graphene of the order 60 T by placing graphene on the ferrimagnetic insulator YIG. From electrical transport measurements, the magnetic order and energy gap of the edge modes in graphene are tunable, and a transition between the canted antiferromagnetic and spin-polarized ferromagnetic $ν = 0$ quantum Hall states can be achieved with relatively low magnetic fields ($> 6$ T) at 2.7 K. The fourth part summarizes the key results of the thesis."],"dc:format.checksum.md5":["2597238f74d2682e0d12b1074eaa4dba","87eda9de84448d1f82354d60eee3eb5f"],"dc:identifier.doi":["10.17863/CAM.48578"],"dc:identifier.uri":["https://www.repository.cam.ac.uk/bitstreams/a0675f87-06ca-4b0e-a580-28862a68cb20/download"],"dc:language":["en"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/301509"],"dc:rights":["https://www.repository.cam.ac.uk/bitstreams/837f6e32-e5bd-4b6b-81fc-011301190621/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"dc:subject":["Graphene","Quantum effect","Edge state","Nonlocal transport","Proximity effect"],"dc:title":["Quantum transport in gapped graphene"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-24T01:33:03Z"}