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Cooper, S. Lance Abbamonte, Peter M. Fradkin, Eduardo H. Stack, John D. Barath, Harini 2010-05-14T20:43:13Z 2010-05-14T20:43:13Z 2012-05-15T10:00:20Z 2010-05-14T20:43:13Z 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. 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No. of bitstreams: 5 Barath_Harini.pdf: 3587151 bytes, checksum: f8700604cc99a25c1755bcddcd9f53fc (MD5) 1_Barath_Harini.pdf: 3587307 bytes, checksum: da8ac60182a9f12ee2a8b553132e5138 (MD5) 2_Barath_Harini.pdf: 3587724 bytes, checksum: 58a3b804b60d09e9482490c6e987903b (MD5) 3_Barath_Harini.pdf: 3587294 bytes, checksum: d7caf4b75595c65be3674b79553a59da (MD5) license.txt: 4061 bytes, checksum: fe6ecebcef892d9e242830456f9fff24 (MD5) Item marked as restricted to the 'Administrator' Group (id=1) by William Ingram (wingram2@illinois.edu) on 2010-05-14T20:45:14Z Item is restricted until 2012-05-14T20:45:13Z Item reinstated by Sarah Shreeves (sshreeve@illinois.edu) on 2012-05-15T10:00:19Z Item was in collections: University of Illinois Dissertations and Theses (ID: 204) Dissertations and Theses - Physics (ID: 445) No. of bitstreams: 6 Barath_Harini.pdf: 3587151 bytes, checksum: f8700604cc99a25c1755bcddcd9f53fc (MD5) 1_Barath_Harini.pdf: 3587307 bytes, checksum: da8ac60182a9f12ee2a8b553132e5138 (MD5) 2_Barath_Harini.pdf: 3587724 bytes, checksum: 58a3b804b60d09e9482490c6e987903b (MD5) 3_Barath_Harini.pdf: 3587294 bytes, checksum: d7caf4b75595c65be3674b79553a59da (MD5) license.txt: 4061 bytes, checksum: fe6ecebcef892d9e242830456f9fff24 (MD5) 3_Barath_Harini.pdf.txt: 154630 bytes, checksum: f36d8fcc41816edb46b67345f47b6092 (MD5) Item released from any restrictions by Sarah Shreeves (sshreeve@illinois.edu) on 2012-05-15T10:00:20Z http://hdl.handle.net/2142/15504 en Copyright 2010 by Harini Barath. All rights reserved. Raman spectroscopy Quantum Phase Transitions Multiferroics Layered Dichalcogenides Superconductivity Inelastic light scattering studies of quantum phase transitions in CuxTiSe2 and multiferroic TbMnO3 2010-5 Physics 1244 Physics 0240 University of Illinois at Urbana-Champaign Dissertation Ph.D. PHD:Physics -UIUC 10KS0240PHD