Dissertation
Symmetry breaking in the correlated electronic and lattice degrees of freedom in the Cu_xTiSe₂ T-x phase diagram
Doctor of Philosophy (Ph.D.), Drexel University
Dec 2017
DOI:
https://doi.org/10.17918/etd-7705
Abstract
In this thesis I investigate the relationship between the charge density wave (CDW) phase and superconductivity in the T-x phase diagram of Cu_xTiSe₂. I find that the incommensurate (IC)-CDW is related to the superconducting phase due to the fact that the former effectively isolates the CDW subsystem degrees of freedom. This increases the symmetry of the electronic populations within the IC-CDW band structure and leave them susceptible to internal instabilities, which in turn give rise to the superconducting phase. Because the correlated properties of these solid-state phases of matter are highly dependent on the crystalline quality of our samples, I also detail the growth of pristine single crystals and utilize several characterization techniques to aid in this purpose. In this portion of the thesis the single crystals are deliberately injected with heat and monitored to deduce the formation of defects through selenium migration. I also confirm the existence of chiral symmetry breaking in the bulk commensurate (C)-CDW phase in TiSe₂ brought about by the cooperation of phonon and exciton degrees of freedom, and also observe chiral character in fluctuations above T_[CDW]. These thermal fluctuations were observed up to 80 K above T_[CDW] via optical signatures of the folded Se-4p band and Raman signatures of the soft L_1^- phonon mode. The suppression of the excitonic degree of freedom with Cu intercalation brings about a quantum phase transition into the IC-CDW at x=0.04. Large quantum fluctuations of the folded Se-4p electronic band were observed at the quantum phase transition where measurements of the phonon system show the onset of incommensuration in the CDW super-lattice. Optical measurements demonstrate a large decoupling of the electron-phonon degrees of freedom within the electronic band structure of the IC-CDW subsystem.
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Details
- Title
- Symmetry breaking in the correlated electronic and lattice degrees of freedom in the Cu_xTiSe₂ T-x phase diagram
- Creators
- David B. Lioi - DU
- Contributors
- Goran Tripun Karapetrov (Advisor) - Drexel University (1970-)Somdev Tyagi (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xvii, 139 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Arts and Sciences; Physics; Drexel University
- Other Identifier
- 7705; 991014632719104721