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Inelastic light scattering study of correlated electron systems

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Title
Inelastic light scattering study of correlated electron systems
Name (type = personal)
NamePart (type = family)
Ye
NamePart (type = given)
Mai
DisplayForm
Mai Ye
Role
RoleTerm (authority = RULIB)
author
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Blumberg
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Girsh
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Girsh Blumberg
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Advisory Committee
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Blumberg
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Girsh
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Girsh Blumberg
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Advisory Committee
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member
Name (type = personal)
NamePart (type = family)
Oh
NamePart (type = given)
Seongshik
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Seongshik Oh
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Advisory Committee
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member
Name (type = personal)
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Zimmermann
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Frank
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Frank Zimmermann
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Advisory Committee
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member
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Gershtein
NamePart (type = given)
Yuri
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Yuri Gershtein
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Advisory Committee
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member
Name (type = personal)
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Sirenko
NamePart (type = given)
Andrei
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Andrei Sirenko
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Advisory Committee
Role
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member
Name (type = corporate)
NamePart
Rutgers University
Role
RoleTerm (authority = RULIB)
degree grantor
Name (type = corporate)
NamePart
School of Graduate Studies
Role
RoleTerm (authority = RULIB)
school
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Text
Genre (authority = marcgt)
theses
OriginInfo
DateCreated (encoding = w3cdtf); (qualifier = exact)
2022
DateOther (encoding = w3cdtf); (type = degree); (qualifier = exact)
2022-01
Language
LanguageTerm (authority = ISO 639-3:2007); (type = text)
English
Abstract (type = abstract)
My thesis study focuses on exploring correlated electron systems by means of inelastic light scattering. Specifically, I investigate quadrupolar fluctuations and crystal-field (CF) excitations in 4f-electron systems, and the nature of unconventional insulating phases in 5d-electron systems. The light-scattering experimental technique offers both high energy resolution and the ability to disentangle the long-wavelength excitation spectra into individual symmetry channels. Such advantages are particularly useful to study the questions focused by my thesis.

Heavy-fermion metal CeB₆ exhibits an antiferroquadrupolar ordering of T<sub>2g</sub> (xy type) symmetry below 3.2K. We perform a comprehensive spectroscopic study of this material, discussing its electronic, magnetic, and phononic excitations. In particular, we find the spectral linewidth of the CF excitations is broadened by Kondo effect, and the tendency towards finite-wavevector quadrupolar ordering induces ferromagnetic correlations which manifest as long-wavelength magnetic fluctuations.

Another heavy-fermion metal, YbRu₂Ge₂, enters a ferroquadrupolar phase of B<sub>1g</sub> (x²-y² type) below 10K. We study the quadrupolar fluctuations, CF excitations, and lattice dynamics of this compound. We show that the electronic static Raman susceptibilities in quadrupolar symmetry channels follow nearly Curie-law behavior; the relatively strong coupling to the lattice in the B<sub>1g</sub> channel enhances the vanishingly small electronic Weiss temperature to the temperature of quadrupole phase transition at 10K.

Ferroelectric insulator TbInO₃ has been proposed to be a spin-liquid candidate. To understand its ground-state property, we study its low-energy CF excitations. We show that the ground state of the Tb³⁺ ions is a non-Kramers doublet. We also demonstrate that the obtained CF level scheme is consistent with specific heat data. In addition, we observe hybrid excitations involving coupled CF and phonon modes, suggesting strong spin-lattice interaction. The complex spin Hamiltonian of TbInO₃ renders this material a suitable platform to investigate the effects of non-Kramers doublet ground state on a triangular magnetic lattice.

Paramagnetic insulator Ba₅CuIr₃O₁₂ hosts face-sharing Ir octahedra forming quasi-one-dimensional chains. We explore the electronic structure of this system. We show that the insulating mechanism of this iridate cannot be described by the commonly-adopted J<sub>eff</sub>=1/2 local moment picture. Instead, the shorter Ir-Ir distance in face-sharing geometry leads to strong covalency between neighboring Ir⁴⁺ ions; this strong covalency results in the formation of molecular orbits as the low-energy electronic degree of freedom. To further illustrate the nature of the insulating state of Ba₅CuIr₃O₁₂, we also study the thermodynamic properties of this compound. While the temperature dependence of the magnetic susceptibility and specific heat suggests weak antiferromagnetic correlations, the magnetization does not saturate up 59T. This phenomenon can be understood in the framework of random singlet state, and we obtain the exchange coupling distribution from the magnetization data.

Zero-gap semiconductor Ta₂NiSe₅ is one promising candidate of excitonic insulator, a coherent electronic phase resulting from the formation of a macroscopic population of excitons. We study its critical excitonic fluctuations and emergent coherence. The quadrupolar excitonic mode exhibits significant softening close to the phase transition, and its coupling to noncritical lattice modes enhances the transition temperature. On cooling, we observe gradual emergence of coherent superpositions of band states at the gap edge. Moreover, we explore the effect of sulfur doping. We find that the critical excitonic fluctuations diminish with the sulfur doping, and eventually shift to high energies, characteristic of a quantum phase transition. However, a symmetry-breaking transition at finite temperatures is detected at all doping level, exposing a cooperating lattice instability that takes over for large doping level. The study therefore reveals a failed excitonic quantum phase transition, masked by a preemptive structural order.
Subject (authority = RUETD)
Topic
Condensed matter physics
Subject (authority = RUETD)
Topic
Materials Science
Subject (authority = RUETD)
Topic
Optics
Subject (authority = local)
Topic
Crystal field
Subject (authority = local)
Topic
Excitonic insulator
Subject (authority = local)
Topic
Heavy fermion
Subject (authority = local)
Topic
Iridate
Subject (authority = local)
Topic
Quadrupole
Subject (authority = local)
Topic
Raman scattering
RelatedItem (type = host)
TitleInfo
Title
Rutgers University Electronic Theses and Dissertations
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http://dissertations.umi.com/gsnb.rutgers:11667
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316 pages : illustrations
Note (type = degree)
Ph.D.
Note (type = bibliography)
Includes bibliographical references
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Title
School of Graduate Studies Electronic Theses and Dissertations
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rucore10001600001
Location
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NjNbRU
Identifier (type = doi)
doi:10.7282/t3-fmzn-8145
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The author owns the copyright to this work.
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Name
FamilyName
Ye
GivenName
Mai
Role
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RightsEvent
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Permission or license
DateTime (encoding = w3cdtf); (qualifier = exact); (point = start)
2022-02-04T13:12:11
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Mai Ye
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Affiliation
Rutgers University. School of Graduate Studies
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I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.
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2021-11-19T18:31:08
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2021-11-19T18:31:08
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