{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/15504"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/15504","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Inelastic light scattering studies of quantum phase transitions in CuxTiSe2 and multiferroic TbMnO3","abstract":"Abstract In this dissertation, inelastic (Raman) light scattering techniques are used to probe the temperature- and magnetic-field-induced phase transitions of two strongly correlated systems – the magnetoelectric multiferroic TbMnO3 and the layered dichalcogenide TiSe2 . In general, strongly correlated materials have a strong coupling between charge, spin, lattice and orbital degrees of freedom. Because of the inter- play between various competing orders, these systems have highly complex phase diagrams and exhibit interesting phenomena such as colossal magnetoresistance (CMR), high temperature superconductivity and charge/orbital ordering (COO). Magnetoelectric multiferroics are an important and interesting sub-class of strongly correlated systems. These are systems whose magnetic and electric orders are strongly coupled, thereby showing exquisite tunability of the electric polarization via applied magnetic fields, and vice-versa. One such system is the perovskite manganite, TbMnO3 , which shows magnetic-field-tuned rearrangement of the electric polarization vector in the ferroelectric phase below a critical temperature, Tc ∼ 28 K. This ferroelectric phase transition is accompanied, and in fact caused, by a magnetic phase transition from an incommensurate spiral magnetic arrangement of the Mn3+ ions to a commensurate magnetic phase as a function of applied field. We use Raman scattering to carefully probe this magnetic-field-tuned phase transition in microscopic detail. Our measurements indicate that field-induced quantum fluctuations of commensurate domains, which likely drive the field-induced polarization flop in this material, are found near the field-tuned incommensurate-commensurate phase transition. The second focus of this dissertation is the study of quantum phase transitions in TiSe2 as a function of temperature and Cu-intercalation, and the comparison of the effects of intercalation and pressure on the charge-density-wave (CDW) order in this system. All these parameters – temperature, pressure and Cu-intercalation – suppress the CDW state in TiSe2 . Our Raman measurements on Cux TiSe2 show that the x-dependent mode softening exhibits identical scaling behavior to thermal mode softening in undoped TiSe2 , suggesting that, like thermal mode softening, the x-dependent mode softening is also associated with a critical point. The softening and significant linewidth broadening of the observed CDW amplitude modes indicate strong fluctuations of the CDW. Even more interesting is the emergence of a superconducting (SC) phase – in Cux TiSe2 and pressure-tuned TiSe2 – indicating a likely coexistence of fluctuating CDW and SC phases near the quantum phase boundary.","abstract_html":"Abstract In this dissertation, inelastic (Raman) light scattering techniques are used to probe the temperature- and magnetic-field-induced phase transitions of two strongly correlated systems – the magnetoelectric multiferroic TbMnO3 and the layered dichalcogenide TiSe2 . In general, strongly correlated materials have a strong coupling between charge, spin, lattice and orbital degrees of freedom. Because of the inter- play between various competing orders, these systems have highly complex phase diagrams and exhibit interesting phenomena such as colossal magnetoresistance (CMR), high temperature superconductivity and charge/orbital ordering (COO). Magnetoelectric multiferroics are an important and interesting sub-class of strongly correlated systems. These are systems whose magnetic and electric orders are strongly coupled, thereby showing exquisite tunability of the electric polarization via applied magnetic fields, and vice-versa. One such system is the perovskite manganite, TbMnO3 , which shows magnetic-field-tuned rearrangement of the electric polarization vector in the ferroelectric phase below a critical temperature, Tc ∼ 28 K. This ferroelectric phase transition is accompanied, and in fact caused, by a magnetic phase transition from an incommensurate spiral magnetic arrangement of the Mn3+ ions to a commensurate magnetic phase as a function of applied field. We use Raman scattering to carefully probe this magnetic-field-tuned phase transition in microscopic detail. Our measurements indicate that field-induced quantum fluctuations of commensurate domains, which likely drive the field-induced polarization flop in this material, are found near the field-tuned incommensurate-commensurate phase transition. The second focus of this dissertation is the study of quantum phase transitions in TiSe2 as a function of temperature and Cu-intercalation, and the comparison of the effects of intercalation and pressure on the charge-density-wave (CDW) order in this system. All these parameters – temperature, pressure and Cu-intercalation – suppress the CDW state in TiSe2 . Our Raman measurements on Cux TiSe2 show that the x-dependent mode softening exhibits identical scaling behavior to thermal mode softening in undoped TiSe2 , suggesting that, like thermal mode softening, the x-dependent mode softening is also associated with a critical point. The softening and significant linewidth broadening of the observed CDW amplitude modes indicate strong fluctuations of the CDW. Even more interesting is the emergence of a superconducting (SC) phase – in Cux TiSe2 and pressure-tuned TiSe2 – indicating a likely coexistence of fluctuating CDW and SC phases near the quantum phase boundary.","abstract_has_math":false,"creators":["Barath, Harini"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Cooper, S. Lance","Abbamonte, Peter M.","Fradkin, Eduardo H.","Stack, John D."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2010,"date_issued":"2010-05-14T20:43:13Z","date_published":"2010-05-14T20:43:13Z","updated_at":"2026-07-22T22:25:08Z","subjects":["Raman spectroscopy","Quantum Phase Transitions","Multiferroics","Layered Dichalcogenides","Superconductivity"],"languages":["en"],"rights":["Copyright 2010 by Harini Barath. All rights reserved."],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/15504","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Cooper, S. 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All rights reserved."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/15504"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Abstract In this dissertation, inelastic (Raman) light scattering techniques are used to probe the temperature- and magnetic-field-induced phase transitions of two strongly correlated systems – the magnetoelectric multiferroic TbMnO3 and the layered dichalcogenide TiSe2 . In general, strongly correlated materials have a strong coupling between charge, spin, lattice and orbital degrees of freedom. Because of the inter- play between various competing orders, these systems have highly complex phase diagrams and exhibit interesting phenomena such as colossal magnetoresistance (CMR), high temperature superconductivity and charge/orbital ordering (COO). Magnetoelectric multiferroics are an important and interesting sub-class of strongly correlated systems. These are systems whose magnetic and electric orders are strongly coupled, thereby showing exquisite tunability of the electric polarization via applied magnetic fields, and vice-versa. One such system is the perovskite manganite, TbMnO3 , which shows magnetic-field-tuned rearrangement of the electric polarization vector in the ferroelectric phase below a critical temperature, Tc ∼ 28 K. This ferroelectric phase transition is accompanied, and in fact caused, by a magnetic phase transition from an incommensurate spiral magnetic arrangement of the Mn3+ ions to a commensurate magnetic phase as a function of applied field. We use Raman scattering to carefully probe this magnetic-field-tuned phase transition in microscopic detail. Our measurements indicate that field-induced quantum fluctuations of commensurate domains, which likely drive the field-induced polarization flop in this material, are found near the field-tuned incommensurate-commensurate phase transition. The second focus of this dissertation is the study of quantum phase transitions in TiSe2 as a function of temperature and Cu-intercalation, and the comparison of the effects of intercalation and pressure on the charge-density-wave (CDW) order in this system. All these parameters – temperature, pressure and Cu-intercalation – suppress the CDW state in TiSe2 . Our Raman measurements on Cux TiSe2 show that the x-dependent mode softening exhibits identical scaling behavior to thermal mode softening in undoped TiSe2 , suggesting that, like thermal mode softening, the x-dependent mode softening is also associated with a critical point. The softening and significant linewidth broadening of the observed CDW amplitude modes indicate strong fluctuations of the CDW. Even more interesting is the emergence of a superconducting (SC) phase – in Cux TiSe2 and pressure-tuned TiSe2 – indicating a likely coexistence of fluctuating CDW and SC phases near the quantum phase boundary.","Item withdrawn by Mark Zulauf (zulauf@illinois.edu) on 2010-04-06T20:46:16Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Barath_Harini.pdf: 3587724 bytes, checksum: 58a3b804b60d09e9482490c6e987903b (MD5)","Made available in DSpace on 2010-05-14T20:43:13Z (GMT). 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Lance","Abbamonte, Peter M.","Fradkin, Eduardo H.","Stack, John D."],"dc:creator":["Barath, Harini"],"dc:date":["2010-05-14T20:43:13Z","2012-05-15T10:00:20Z","2010-5"],"dc:description":["Abstract In this dissertation, inelastic (Raman) light scattering techniques are used to probe the temperature- and magnetic-field-induced phase transitions of two strongly correlated systems – the magnetoelectric multiferroic TbMnO3 and the layered dichalcogenide TiSe2 . In general, strongly correlated materials have a strong coupling between charge, spin, lattice and orbital degrees of freedom. Because of the inter- play between various competing orders, these systems have highly complex phase diagrams and exhibit interesting phenomena such as colossal magnetoresistance (CMR), high temperature superconductivity and charge/orbital ordering (COO). Magnetoelectric multiferroics are an important and interesting sub-class of strongly correlated systems. These are systems whose magnetic and electric orders are strongly coupled, thereby showing exquisite tunability of the electric polarization via applied magnetic fields, and vice-versa. One such system is the perovskite manganite, TbMnO3 , which shows magnetic-field-tuned rearrangement of the electric polarization vector in the ferroelectric phase below a critical temperature, Tc ∼ 28 K. This ferroelectric phase transition is accompanied, and in fact caused, by a magnetic phase transition from an incommensurate spiral magnetic arrangement of the Mn3+ ions to a commensurate magnetic phase as a function of applied field. We use Raman scattering to carefully probe this magnetic-field-tuned phase transition in microscopic detail. Our measurements indicate that field-induced quantum fluctuations of commensurate domains, which likely drive the field-induced polarization flop in this material, are found near the field-tuned incommensurate-commensurate phase transition. The second focus of this dissertation is the study of quantum phase transitions in TiSe2 as a function of temperature and Cu-intercalation, and the comparison of the effects of intercalation and pressure on the charge-density-wave (CDW) order in this system. All these parameters – temperature, pressure and Cu-intercalation – suppress the CDW state in TiSe2 . Our Raman measurements on Cux TiSe2 show that the x-dependent mode softening exhibits identical scaling behavior to thermal mode softening in undoped TiSe2 , suggesting that, like thermal mode softening, the x-dependent mode softening is also associated with a critical point. The softening and significant linewidth broadening of the observed CDW amplitude modes indicate strong fluctuations of the CDW. Even more interesting is the emergence of a superconducting (SC) phase – in Cux TiSe2 and pressure-tuned TiSe2 – indicating a likely coexistence of fluctuating CDW and SC phases near the quantum phase boundary.","Item withdrawn by Mark Zulauf (zulauf@illinois.edu) on 2010-04-06T20:46:16Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Barath_Harini.pdf: 3587724 bytes, checksum: 58a3b804b60d09e9482490c6e987903b (MD5)","Made available in DSpace on 2010-05-14T20:43:13Z (GMT). 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All rights reserved."],"dc:subject":["Raman spectroscopy","Quantum Phase Transitions","Multiferroics","Layered Dichalcogenides","Superconductivity"],"dc:title":["Inelastic light scattering studies of quantum phase transitions in CuxTiSe2 and multiferroic TbMnO3"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:08Z"}