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Title:Light scattering studies of magnetostructural phases in Mn3O4 and charge density wave melting in ZrTe3
Author(s):Gleason, Samuel Lawrence
Director of Research:Cooper, Lance
Doctoral Committee Chair(s):MacDougall, Gregory
Doctoral Committee Member(s):Phillips, Philip; Eckstein, James
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
light scattering
charge density wave
Abstract:In this thesis, variable-magnetic-field and variable-pressure Raman spectroscopy is used to study the magnetically ordered phases of magnetodielectric Mn3O4, as well as the pressure-induced charge-ordered to superconducting transition in ZrTe3. In Mn3O4, I examine the differences in magnetic and structural order between two distinct orthorhombic phases which are descended from the paramagnetic tetragonal phase. These two orthorhombic phases are nearly degenerate and intrinsically coexist at low temperatures. I demonstrate that magnetic fields directed along the secondary and tertiary tetragonal directions stabilize the first and second orthorhombic phases, respectively, and compare these results to magnetic-field-induced changes in the bulk dielectric response. These are the first spectroscopic measurements of untwinned crystals of Mn3O4, which were grown directly into the tetragonally distorted spinel phase, thereby avoiding twinning associated with the high-temperature Jahn-Teller distortion. For comparison, I present measurements of Mn3O4 under pressure, as well as measurements of twinned Mn3O4, to show how strain can dramatically affect the orthorhombic phase coexistence. Strain may provide a novel method of tuning the bulk behavior of materials like Mn3O4 that display nanoscale inhomogeneity. In ZrTe3, I observe enormous increases in select phonon lifetimes concomitant with charge density wave (CDW) formation, which indicates that these phonons are strongly coupled to regions of the Fermi surface that are gapped by the CDW. These strongly-coupled phonons involve internal vibrations of ZrTe3 prismatic rods. Applying pressure progressively removes spectral weight from peaks that represent the strongly coupled internal vibrations as the system approaches the CDW-to-superconducting transition at P = 50 kbar. I argue that this reduction in spectral weight indicates a loss of long-range order within the ZrTe3 rods, specifically among intrarod Zr-Te bonds. Together, these results suggest that the pressure-induced suppression of CDW order in ZrTe3 is driven by crystallographic disorder.
Issue Date:2018-04-18
Rights Information:Copyright 2018 Samuel Gleason
Date Available in IDEALS:2018-09-04
Date Deposited:2018-05

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