{"id":{"repo_id":"mit","oai_identifier":"oai:dspace.mit.edu:1721.1/157577"},"canonical_url":"https://search.dev.ndltd.org/etd/mit/oai:dspace.mit.edu:1721.1/157577","repository":{"repo_id":"mit","name":"MIT","base_url":"https://dspace.mit.edu/oai/request"},"display":{"title":"Spectroscopic study of emergent electronic phases in transition metal based compounds","abstract":"Antiferromagnets with non-relativistic spin splitting are outstanding candidates as the next generation of spintronic materials owing to their electron-volt (eV) scale spin splitting, ultrafast spin dynamics and nearly vanishing stray fields. Achieving voltage-based control of spin polarization in antiferromagnets is of great interest for realizing energy-efficient and compact devices for information storage and processing. Spin spiral type-II multiferroics exhibit an inversion-symmetry-breaking antiferromagnetic order which directly induces ferroelectric polarization, allowing for symmetry protected cross-control between spin chirality and polar order. This intrinsic coupling between the magnetic and dipolar order parameters results in record-strength magnetoelectric effects. Two-dimensional materials possessing such intrinsic multiferroic properties have been long sought for harnessing magnetoelectric coupling in nanoelectronic devices. The recent discovery of intrinsic magnetic order in atomically-thin van der Waals (vdW) materials has created new opportunities for the study of collective spin phenomena in free-standing two-dimensional (2D) systems and nanoscale devices. Among possible multiferroic vdW materials, several families have been identified, and of particular promise is the magnetic semiconductor NiI₂. The multiferroic state of NiI₂ is characterized by a proper-screw spin helix with given handedness, which couples to the charge degrees of freedom to produce a chirality-controlled electrical polarization. We use a suite of optical technique which reveal an ordered magnetic, polar state that persists down to the ultrathin limit of monolayer NiI₂. Recent development of spin-group formalism has identified a new class of magnets with nontrivial spin textures, including even-parity d, g, or i-wave altermagnet and odd-parity p-wave antiferromagnets. The chiral magnetic order in NiI₂ breaks Inversion-Time-Reversal-Translation (P Tτ ) symmetry, and Spin-Rotation-Translation (Uτ ) symmetry, allowing for spin splitting even in the absence of spin-orbit-coupling (SOC). We provide direct evidence that the spin polarization in a spin spiral type-II multiferroic exhibits p-wave (odd-parity) character and directly couples to the spin chirality, enabling electrical control of non-relativistic spin splitting. Our findings represent the first observation of a p-wave antiferromagnet, and open a new frontier of voltage-based switching of non-relativistic spin splitting in vdW antiferromagnets.","abstract_html":"Antiferromagnets with non-relativistic spin splitting are outstanding candidates as the next generation of spintronic materials owing to their electron-volt (eV) scale spin splitting, ultrafast spin dynamics and nearly vanishing stray fields. Achieving voltage-based control of spin polarization in antiferromagnets is of great interest for realizing energy-efficient and compact devices for information storage and processing. Spin spiral type-II multiferroics exhibit an inversion-symmetry-breaking antiferromagnetic order which directly induces ferroelectric polarization, allowing for symmetry protected cross-control between spin chirality and polar order. This intrinsic coupling between the magnetic and dipolar order parameters results in record-strength magnetoelectric effects. Two-dimensional materials possessing such intrinsic multiferroic properties have been long sought for harnessing magnetoelectric coupling in nanoelectronic devices. The recent discovery of intrinsic magnetic order in atomically-thin van der Waals (vdW) materials has created new opportunities for the study of collective spin phenomena in free-standing two-dimensional (2D) systems and nanoscale devices. Among possible multiferroic vdW materials, several families have been identified, and of particular promise is the magnetic semiconductor NiI₂. The multiferroic state of NiI₂ is characterized by a proper-screw spin helix with given handedness, which couples to the charge degrees of freedom to produce a chirality-controlled electrical polarization. We use a suite of optical technique which reveal an ordered magnetic, polar state that persists down to the ultrathin limit of monolayer NiI₂. Recent development of spin-group formalism has identified a new class of magnets with nontrivial spin textures, including even-parity d, g, or i-wave altermagnet and odd-parity p-wave antiferromagnets. The chiral magnetic order in NiI₂ breaks Inversion-Time-Reversal-Translation (P Tτ ) symmetry, and Spin-Rotation-Translation (Uτ ) symmetry, allowing for spin splitting even in the absence of spin-orbit-coupling (SOC). We provide direct evidence that the spin polarization in a spin spiral type-II multiferroic exhibits p-wave (odd-parity) character and directly couples to the spin chirality, enabling electrical control of non-relativistic spin splitting. Our findings represent the first observation of a p-wave antiferromagnet, and open a new frontier of voltage-based switching of non-relativistic spin splitting in vdW antiferromagnets.","abstract_has_math":false,"creators":["Song, Qian"],"institution":"Massachusetts Institute of Technology","degree_name":"Doctoral","degree_level":null,"degree_discipline":null,"degree_department":"Massachusetts Institute of Technology. Department of Materials Science and Engineering","school":null,"contributors":[],"advisors":["Comin, Riccardo"],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-09","date_published":"2024-09","updated_at":"2026-07-22T22:21:48Z","subjects":[],"languages":[],"rights":["In Copyright - Educational Use Permitted","Copyright retained by author(s)"],"rights_urls":["https://rightsstatements.org/page/InC-EDU/1.0/"],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/1721.1/157577","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Comin, Riccardo"]},{"key":"dc:contributor.department","label":"Department","values":["Massachusetts Institute of Technology. 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Achieving voltage-based control of spin polarization in antiferromagnets is of great interest for realizing energy-efficient and compact devices for information storage and processing. Spin spiral type-II multiferroics exhibit an inversion-symmetry-breaking antiferromagnetic order which directly induces ferroelectric polarization, allowing for symmetry protected cross-control between spin chirality and polar order. This intrinsic coupling between the magnetic and dipolar order parameters results in record-strength magnetoelectric effects. Two-dimensional materials possessing such intrinsic multiferroic properties have been long sought for harnessing magnetoelectric coupling in nanoelectronic devices. The recent discovery of intrinsic magnetic order in atomically-thin van der Waals (vdW) materials has created new opportunities for the study of collective spin phenomena in free-standing two-dimensional (2D) systems and nanoscale devices. Among possible multiferroic vdW materials, several families have been identified, and of particular promise is the magnetic semiconductor NiI₂. The multiferroic state of NiI₂ is characterized by a proper-screw spin helix with given handedness, which couples to the charge degrees of freedom to produce a chirality-controlled electrical polarization. We use a suite of optical technique which reveal an ordered magnetic, polar state that persists down to the ultrathin limit of monolayer NiI₂. Recent development of spin-group formalism has identified a new class of magnets with nontrivial spin textures, including even-parity d, g, or i-wave altermagnet and odd-parity p-wave antiferromagnets. The chiral magnetic order in NiI₂ breaks Inversion-Time-Reversal-Translation (P Tτ ) symmetry, and Spin-Rotation-Translation (Uτ ) symmetry, allowing for spin splitting even in the absence of spin-orbit-coupling (SOC). We provide direct evidence that the spin polarization in a spin spiral type-II multiferroic exhibits p-wave (odd-parity) character and directly couples to the spin chirality, enabling electrical control of non-relativistic spin splitting. Our findings represent the first observation of a p-wave antiferromagnet, and open a new frontier of voltage-based switching of non-relativistic spin splitting in vdW antiferromagnets."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph.D."]},{"key":"dc:title","label":"Title","values":["Spectroscopic study of emergent electronic phases in transition metal based compounds"]}]}],"canonical_facts":{"dc:contributor.advisor":["Comin, Riccardo"],"dc:contributor.department":["Massachusetts Institute of Technology. Department of Materials Science and Engineering"],"dc:creator":["Song, Qian"],"dc:date.accessioned":["2024-11-18T19:11:59Z"],"dc:date.available":["2024-11-18T19:11:59Z"],"dc:date.issued":["2024-09"],"dc:description.abstract":["Antiferromagnets with non-relativistic spin splitting are outstanding candidates as the next generation of spintronic materials owing to their electron-volt (eV) scale spin splitting, ultrafast spin dynamics and nearly vanishing stray fields. Achieving voltage-based control of spin polarization in antiferromagnets is of great interest for realizing energy-efficient and compact devices for information storage and processing. Spin spiral type-II multiferroics exhibit an inversion-symmetry-breaking antiferromagnetic order which directly induces ferroelectric polarization, allowing for symmetry protected cross-control between spin chirality and polar order. This intrinsic coupling between the magnetic and dipolar order parameters results in record-strength magnetoelectric effects. Two-dimensional materials possessing such intrinsic multiferroic properties have been long sought for harnessing magnetoelectric coupling in nanoelectronic devices. The recent discovery of intrinsic magnetic order in atomically-thin van der Waals (vdW) materials has created new opportunities for the study of collective spin phenomena in free-standing two-dimensional (2D) systems and nanoscale devices. Among possible multiferroic vdW materials, several families have been identified, and of particular promise is the magnetic semiconductor NiI₂. The multiferroic state of NiI₂ is characterized by a proper-screw spin helix with given handedness, which couples to the charge degrees of freedom to produce a chirality-controlled electrical polarization. We use a suite of optical technique which reveal an ordered magnetic, polar state that persists down to the ultrathin limit of monolayer NiI₂. Recent development of spin-group formalism has identified a new class of magnets with nontrivial spin textures, including even-parity d, g, or i-wave altermagnet and odd-parity p-wave antiferromagnets. The chiral magnetic order in NiI₂ breaks Inversion-Time-Reversal-Translation (P Tτ ) symmetry, and Spin-Rotation-Translation (Uτ ) symmetry, allowing for spin splitting even in the absence of spin-orbit-coupling (SOC). We provide direct evidence that the spin polarization in a spin spiral type-II multiferroic exhibits p-wave (odd-parity) character and directly couples to the spin chirality, enabling electrical control of non-relativistic spin splitting. Our findings represent the first observation of a p-wave antiferromagnet, and open a new frontier of voltage-based switching of non-relativistic spin splitting in vdW antiferromagnets."],"dc:description.degree":["Ph.D."],"dc:identifier.uri":["https://hdl.handle.net/1721.1/157577"],"dc:publisher":["Massachusetts Institute of Technology"],"dc:rights":["In Copyright - Educational Use Permitted","Copyright retained by author(s)"],"dc:rights.uri":["https://rightsstatements.org/page/InC-EDU/1.0/"],"dc:title":["Spectroscopic study of emergent electronic phases in transition metal based compounds"],"dc:type":["Thesis"],"thesis:degree_name":["Doctoral","Doctor of Philosophy"]},"updated_at":"2026-07-22T22:21:48Z"}