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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Optical Studies of Metamaterials and Bosonic Spectra of High-Tc Superconductors

Yang, Jing January 2008 (has links)
The optical spectroscopy techniques have been used to investigate left-handed behavior of metamaterials as well as the electron-bosonic spectral functions (or Bosonic spectra) of high-transition-temperature superconductors (or high-Tc superconductors) in the research work of this thesis. The periodic double-ring split-ring resonator (SRR) array was one of the first proposed magnetic metamaterials which could give rise to a negative magnetic permeability (μ<0). In the traditional design of negative index metamaterials, the SRR arrays were combined with continuous metallic wires that provide a negative electric permittivity (∊<0). However, the requirement of an unbroken electrical connection between unit cells would be challenging in building contoured devices. In our study, we carefully examine the electromagnetic properties of the double-ring SRR arrays on silicon substrates in the mid-infrared frequency regime experimentally and numerically. For light at normal incidence, we observe that an electric resonance in the outer ring and a magnetic resonance in the inner ring exist at similar frequencies in one of our samples, which suggests that the double-ring SRR array could have simultaneous a negative permittivity and a negative permeability, or a left-handed behavior. Our conjectures are confirmed by the numerical simulations. We also propose a new left-handed metamaterial composed of two single-ring SRRs in each unit cell. The left-handed behaviors in our designs originate from the SRR structure itself only and therefore, there are no metallic continuous wires involved compared to the conventional left-handed SRR metamaterials. The high-Tc superconductor samples studied here are highly under-doped YBa2Cu3O6.35 (YBCO6.35), nearly optimally doped monolayer HgBa2CuO4+ઠ (Hg1201), Zn- and Ni- doped Bi2Sr2CaCu2O8+ઠ (Bi2212) single crystals. We experimentally determine the optical constants of the samples and numerically extract the electronboson spectral functions from the optical scattering rate by either an analytic formula or a maximum entropy inversion technique. We find that the bosonic mode obtained from the optical data is consistent with a peak in the q-averaged susceptibility seen in the magnetic neutron scattering studies. The comparisons of the bosonic spectra between YBCO6.35 and YBCO6.50, monolayer Hg1201 and trilayer Hg1223 (HgBa2Ca2Cu3O8+ઠ), Zn-doped and Ni-doped Bi2212 characterize the variation of the bosonic spectra with the hole concentration, Tc as well as the magnetic and nonmagnetic atom substitution. / Thesis / Doctor of Philosophy (PhD)

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