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You searched for +publisher:"Victoria University of Wellington" +contributor:("Tallon, Jeff"). Showing records 1 – 3 of 3 total matches.

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Victoria University of Wellington

1. Williams, Keryn Anne. High Temperature Superconductors Through the Van Hove Singularity.

Degree: 2009, Victoria University of Wellington

The antibonding VHS of the high temperature superconductor Bi-2212 appears in the extreme overdoped regime, a part of the cuprate phase diagram little studied to date. Observation of this VHS motivated taking a fresh look at the cuprates using fundamentals of electronics as the foundation for understanding the physics involved in the superconductivity of these materials. In the study of the high temperature superconductors it appears important questions have been overlooked, notably the possible contribution of the gapped state and whether these materials are better considered as doped semiconductors rather than as 'poor' metals. We also find the question of the contribution of oxygen, a substance with a strong magnetic signature, to data of the oxygen-doped cuprates has been neglected. Comparison with non-oxygen doping is supportive of the view the oxygen dopant contributes noticeably to magnetic data. Through magnetic susceptibility measurements the antibonding VHS location, predicted by use of Fermi liquid theory, is well confirmed in polycrystals of the lead-doped cuprate Bi-2212. It was found that the peak in the DOS at the VHS produces no corresponding local peak in the critical temperature versus doping. Instead, the VHS appears associated with the disappearance of the superconductivity, rather than with the maximum critical temperature. We find the metal-insulator transition plays an important role. There are two of these in the cuprates, a horizontal doping dependent one and a vertical temperature dependent one. They affect each other. Noting the consequences of doping an insulator until a metallic state is reached enables a connection to be made between doping and pressure. Three requirements are identified for superconductivity to occur: 1. screening 2. pairing 3. charge mobility Each requirement may be separately satisfied in a manner whereby each can vary differently as a function of the same variable. The superconductivity of the cuprates is found to arise out of an underlying non-metallic state. As such, BCS theory, being formulated to explain superconductivity arising from metallic conduction, cannot be directly applicable. However, although HTS materials are a rich repository of both novel and familiar solid state physics, evidence does not appear to support the notion that superconductivity in the cuprates is caused by "exotic" physics. We also find cause for optimism regarding the development of new or improved superconducting materials. Advisors/Committee Members: Tallon, Jeff.

Subjects/Keywords: Van Hove singularity; Superconductivity; High temperature superconductors

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APA (6th Edition):

Williams, K. A. (2009). High Temperature Superconductors Through the Van Hove Singularity. (Masters Thesis). Victoria University of Wellington. Retrieved from http://hdl.handle.net/10063/1345

Chicago Manual of Style (16th Edition):

Williams, Keryn Anne. “High Temperature Superconductors Through the Van Hove Singularity.” 2009. Masters Thesis, Victoria University of Wellington. Accessed March 24, 2019. http://hdl.handle.net/10063/1345.

MLA Handbook (7th Edition):

Williams, Keryn Anne. “High Temperature Superconductors Through the Van Hove Singularity.” 2009. Web. 24 Mar 2019.

Vancouver:

Williams KA. High Temperature Superconductors Through the Van Hove Singularity. [Internet] [Masters thesis]. Victoria University of Wellington; 2009. [cited 2019 Mar 24]. Available from: http://hdl.handle.net/10063/1345.

Council of Science Editors:

Williams KA. High Temperature Superconductors Through the Van Hove Singularity. [Masters Thesis]. Victoria University of Wellington; 2009. Available from: http://hdl.handle.net/10063/1345


Victoria University of Wellington

2. McCann, Duncan Michael. Thermodynamics and Strong-coupling Superconducting Energy Gaps.

Degree: 2013, Victoria University of Wellington

Superconductivity is a field where much research has been conducted into explaining all aspects of this phenomenon in many materials. BCS theory provided the principal understanding of superconductivity in conventional materials yet fails to entirely describe those which exhibit greater coupling-strengths as well as the more unconventional superconductors. Formulations have been proposed which extend BCS theory in various ways such as scaling the predicted energy gap by values representative of greater coupling strengths. In order to further extend such formulations we applied our own theory which recalculates the energy gap based solely on thermodynamic parameters, in the hope of improving their accuracy. Comparisons of this energy gap calculated from existing critical-field measurements as well as computational predictions for a range of weak- to strong-coupling type I s-wave superconductors were made with experimental tunnelling measurements. Our thermodynamic theory provided an accurate temperature-dependence of the energy gap for all these superconductors except for the strongest coupler which produced erroneous predictions. An extra-strong-coupling superconductor Pb₀.₇Bi₀.₃ was synthesised and it’s critical-field measured in order to rigorously test our theory in the strong-coupling regime. It exhibited type II superconductivity contrary to our belief and as such measurements were insufficient for an accurate comparison. However, computational calculations predicted an accurate temperature-dependence for the energy gap of Pb₀.₇Bi₀.₃ when compared with experimental tunnelling measurements. Thus our theory appears to apply for this extra-strong-coupling type II superconductor and not for the strong-coupling type I superconductor, which prompts further investigation. These comparisons depend upon the accuracy with which the temperature-dependence of the energy gap can be measured - not an easy task. Extension was also made to d-wave superconductivity where our theory provided little improvement over a scaled BCS interpretation for several overdoped samples of the unconventional Bi-2212 superconductor. However, and this is a most important conclusion, this is due to the weak nature of the coupling in this material which we were able to establish. Thus our theory appears to provide several promising first-order results and warrants further investigation and application to a range of superconductors. Advisors/Committee Members: Tallon, Jeff, Kaiser, Alan.

Subjects/Keywords: Superconductivity; Coupling; Energy gap

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

McCann, D. M. (2013). Thermodynamics and Strong-coupling Superconducting Energy Gaps. (Masters Thesis). Victoria University of Wellington. Retrieved from http://hdl.handle.net/10063/2931

Chicago Manual of Style (16th Edition):

McCann, Duncan Michael. “Thermodynamics and Strong-coupling Superconducting Energy Gaps.” 2013. Masters Thesis, Victoria University of Wellington. Accessed March 24, 2019. http://hdl.handle.net/10063/2931.

MLA Handbook (7th Edition):

McCann, Duncan Michael. “Thermodynamics and Strong-coupling Superconducting Energy Gaps.” 2013. Web. 24 Mar 2019.

Vancouver:

McCann DM. Thermodynamics and Strong-coupling Superconducting Energy Gaps. [Internet] [Masters thesis]. Victoria University of Wellington; 2013. [cited 2019 Mar 24]. Available from: http://hdl.handle.net/10063/2931.

Council of Science Editors:

McCann DM. Thermodynamics and Strong-coupling Superconducting Energy Gaps. [Masters Thesis]. Victoria University of Wellington; 2013. Available from: http://hdl.handle.net/10063/2931


Victoria University of Wellington

3. Ingham, Bridget. Low-Dimensional Physics of Organic-Inorganic Multilayers.

Degree: 2005, Victoria University of Wellington

This thesis demonstrates the rich low-dimensional physics associated with the class of organic-inorganic hybrid materials based on atomic layers of a metal oxide separated by organic spacer molecules. Hybrid materials based on tungsten oxide and also transition metal tungstates (with manganese, iron, cobalt, nickel and copper) were synthesised and characterised using a variety of techniques. The materials in question represent one example of the huge variety of systems classed as 'organic-inorganic hybrids' and have the potential to combine the high-electron mobility of the metal oxide layers with the propensity for self-assembly of the organic layers. The crystal structures of the compounds were investigated using powder X-ray diffraction and electron diffraction, and compared with structural information obtained using IR, Raman, and extended X-ray absorption fine structure (EXAFS) spectroscopies. This data confirmed the presence of a 2- dimensional layered structure. The electronic properties of the hybrids were studied using optical spectroscopy and confirmed via ab initio calculations. The band gaps of the tungsten oxide hybrids were found to be independent of interlayer spacing, and in all cases were larger than that observed in the three dimensional WO3 'parent' material. For the transition metal tungstate hybrids there appeared to be significant interactions between the organic amines and the transition metal ions within the inorganic layers. The magnetic properties of the hybrids incorporating transition metal ions were also studied in detail. Many of these metal tungstate hybrids display magnetic transitions at low temperatures indicating a crossover from 2-dimensional to 3-dimensional behaviour. This illustrates the importance of the low-dimensional nature of the inorganic layers in these hybrid materials and thus their potential in nano-structural applications. Advisors/Committee Members: Kaiser, Alan, Tallon, Jeff.

Subjects/Keywords: Solid state physics; Electronic systems; Electronic behaviour

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Ingham, B. (2005). Low-Dimensional Physics of Organic-Inorganic Multilayers. (Doctoral Dissertation). Victoria University of Wellington. Retrieved from http://hdl.handle.net/10063/359

Chicago Manual of Style (16th Edition):

Ingham, Bridget. “Low-Dimensional Physics of Organic-Inorganic Multilayers.” 2005. Doctoral Dissertation, Victoria University of Wellington. Accessed March 24, 2019. http://hdl.handle.net/10063/359.

MLA Handbook (7th Edition):

Ingham, Bridget. “Low-Dimensional Physics of Organic-Inorganic Multilayers.” 2005. Web. 24 Mar 2019.

Vancouver:

Ingham B. Low-Dimensional Physics of Organic-Inorganic Multilayers. [Internet] [Doctoral dissertation]. Victoria University of Wellington; 2005. [cited 2019 Mar 24]. Available from: http://hdl.handle.net/10063/359.

Council of Science Editors:

Ingham B. Low-Dimensional Physics of Organic-Inorganic Multilayers. [Doctoral Dissertation]. Victoria University of Wellington; 2005. Available from: http://hdl.handle.net/10063/359

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