Current Search: superconductivity (x)
View All Items
 Title
 ANGULAR DEPENDENCE OF THE EMISSION FROM THE INTRINSIC JOSEPHSON JUNCTION IN PIESHAPED WEDGE TRIANGULAR BSCCO MESAS.
 Creator

Morales, Manuel, Klemm, Richard, University of Central Florida
 Abstract / Description

The purpose of this thesis is to determine the radiation patterns from an acute isosceles triangular superconducting mesa modeled by a pieshaped geometry. The terahertz band lies between the microwave and infrared regions of the electromagnetic spec trum. The terahertz radiation from atomicscale layered superconducting mesas is caused by the tunneling of electron pairs in the acJosephson effect. To determine the terahertz power radiated per unit solid angle of an acute isosceles...
Show moreThe purpose of this thesis is to determine the radiation patterns from an acute isosceles triangular superconducting mesa modeled by a pieshaped geometry. The terahertz band lies between the microwave and infrared regions of the electromagnetic spec trum. The terahertz radiation from atomicscale layered superconducting mesas is caused by the tunneling of electron pairs in the acJosephson effect. To determine the terahertz power radiated per unit solid angle of an acute isosceles triangular superconducting mesa, a model was employed in which the shape of the mesa is approximated as a pieshaped wedge. This model is shown to have an accuracy of about 1%. Using Love's Equivalency Principle, the current caused by the Josephson effect is then assumed to be on the edges of the mesa. Since in the mesas used for experiments the electric field is in the direction of the current, it is parallel to the boundary of the sample. Hence, we want the TM modes, and that requires the magnetic field to be transverse to the boundary. We thus require that the tangential component of the magnetic field parallel at the boundary vanishes. Love's equivalency principle provides the easiest and most straight forward way to satisfy this condition. The surface electric current density was modeled by comparing the magnetic vector potential re sulting from the modeled edge current with that given by a standard volume average integration technique. The surface current density that provided the best approximation to the bulk average was used and the radiation patterns were plotted using Mathematica software.
Show less  Date Issued
 2015
 Identifier
 CFH0004762, ucf:45345
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFH0004762
 Title
 Microscopic Theory of the Knight Shift.
 Creator

Hall, Bianca, Klemm, Richard, Fernandez, Yan, Rahman, Talat, Del Barco, Enrique, Shivamoggi, Bhimsen, University of Central Florida
 Abstract / Description

This dissertation is the beginning of the development of a microscopic theory of the Knight shift. The Knight shift experiment has been used in superconductivity research throughout history, however, a complete understanding of the Knight shift in conventional as well as unconventional superconductors does not yet exist. Motivated by the results of a literature review, which discusses Knight shift anomalies in multiple superconducting materials, this research studies a new model of the Knight...
Show moreThis dissertation is the beginning of the development of a microscopic theory of the Knight shift. The Knight shift experiment has been used in superconductivity research throughout history, however, a complete understanding of the Knight shift in conventional as well as unconventional superconductors does not yet exist. Motivated by the results of a literature review, which discusses Knight shift anomalies in multiple superconducting materials, this research studies a new model of the Knight shift, which involves the processes involved in nuclear magnetic resonance measurements in metals.The result of this study is a microscopic model of nuclear magnetic resonance in metals. The spins of the spin1/2 local nucleus and its surrounding orbital electrons interact with the arbitrary constant ${\bf B}_0$ and perpendicular timeoscillatory magnetic inductions ${\bf B}_1(t)$ and with each other via an anisotropic hyperfine interaction. An Andersonlike Hamiltonian describes the excitations of the relevant occupied local orbital electrons into the conduction bands, each described by an anisotropic effective mass with corresponding Landau orbits and an anisotropic spin ${\bf g}$ tensor. Local orbital electron correlation effects are included using the meanfield decoupling procedure of Lacroix. The metallic contributions to the Knight shift resonance frequency and linewidth shifts are evaluated to leading orders in the hyperfine and Anderson excitation interactions. While respectively proportional to $(B_1/B_0)^2$ and a constant for weak $B_0(>)(>)B_1$, both shifts are shown to depend strongly upon ${\bf B}_0$ when a Landau level is near the Fermi energy.
Show less  Date Issued
 2015
 Identifier
 CFE0005954, ucf:50808
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005954
 Title
 POWER DISTRIBUTION OF TERAHERTZ EMISSION FROM HEXAGONAL BSCCO MICROSTRIP ANTENNAS.
 Creator

Davis, Andrew E, Klemm, Richard, University of Central Florida
 Abstract / Description

We analyze the distribution of coherent terahertz radiation from a regular hexagonal microstrip antenna (MSA) made from the highTc superconductor Bi2Sr2CaCu2O8+x (BSCCO). We discuss the C6v symmetry of the solutions of the wave equation on a hexagonal domain and distinguish between the closedform and nonclosedform solutions. The closedform wavefunctions of the transverse magnetic (TM) electromagnetic cavity modes are presented and formulas for the radiated power arising from the uniform...
Show moreWe analyze the distribution of coherent terahertz radiation from a regular hexagonal microstrip antenna (MSA) made from the highTc superconductor Bi2Sr2CaCu2O8+x (BSCCO). We discuss the C6v symmetry of the solutions of the wave equation on a hexagonal domain and distinguish between the closedform and nonclosedform solutions. The closedform wavefunctions of the transverse magnetic (TM) electromagnetic cavity modes are presented and formulas for the radiated power arising from the uniform part of the AC Josephson current and from the resonant cavity modes are derived. The wavefunctions and angular distribution of radiation from both sources are plotted for sixteen of the lowestenergy modes. Finally, we comment on the relevance of these power distributions to hexagonal arrays of equilateral triangular MSAs and propose a strategy for studying the nonclosedform modes.
Show less  Date Issued
 2017
 Identifier
 CFH2000241, ucf:46016
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFH2000241
 Title
 Novel properties of ferromagnetic pwave superconductors.
 Creator

Lorscher, Christopher, Klemm, Richard, Leuenberger, Michael, Rahman, Talat, Schoenfeld, Winston, University of Central Florida
 Abstract / Description

This thesis investigates the many extraordinary physical properties of the candidate pwave ferromagnetic superconductors UCoGe and URhGe, and proposes theoretical predictions for pwave superconductors yet to be discovered. In particular, we carry out angular dependent quantum field theoretical calculations of the thermodynamic H  T phase diagram known as the upper critical field, or more appropriately for ferromagnetic superconductors the upper critical induction, for various pwave...
Show moreThis thesis investigates the many extraordinary physical properties of the candidate pwave ferromagnetic superconductors UCoGe and URhGe, and proposes theoretical predictions for pwave superconductors yet to be discovered. In particular, we carry out angular dependent quantum field theoretical calculations of the thermodynamic H  T phase diagram known as the upper critical field, or more appropriately for ferromagnetic superconductors the upper critical induction, for various pwave superconducting order parameter symmetries including: The axial AndersonBrinkmanMorel(ABM) state, the chiral ScharnbergKlemm (SK) state, and the completely broken symmetry polar state (CBS), as well as for some other states with partially broken symmetry (PBS) superconducting order parameter symmetries. The most notable contribution of the work presented in this thesis is the application of the KlemmClem transformations to analytically calculate the full angular and temperature dependencies of the upper critical field for orthorhombic materials, which may prove to be useful to experimentalists in identifying these exotic states of matter experimentally. Second, this work formulates a double spinsplit ellipsoidal Fermi surface (FS) model for ferromagnetic superconductors in the normal state, which introduces a field dependence to the effective mass in one crystallographic direction on the dominant Fermi surface and to the chemical potential, and is subsequently applied to the normal state of URhGe to explain theoretically the anomalous specific heat data of Aoki and Flouquet. Extension of this work to understanding the still elusive reentrant highfield superconducting phase of URhGe and the Sshaped upper critical field curve for external magnetic field parallel to the baxis direction inUCoGe is discussed. Third, this work also presents theoretical fits to the upper critical field data of Kittika et al. for Sr2RuO4 using the helical pwave states and including Pauli limiting effects of the three components of the triplet pairspin fixed to the highly conducting layers by strong spinorbit coupling.
Show less  Date Issued
 2014
 Identifier
 CFE0005371, ucf:50451
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005371
 Title
 THE EFFECT OF IMPURITIES ON THE SUPERCONDUCTIVITY OF BSCCO2212.
 Creator

Vastola, John, Klemm, Richard, University of Central Florida
 Abstract / Description

BSCCO2212 is a hightemperature cuprate superconductor whose microscopic behavior is currently poorly understood. In particular, it is unclear whether its order parameter is consistent with swave or dwave symmetry. It has been suggested that its order parameter might take one of several forms that are consistent with dwave behavior. We present some calculations using the manybody theory approach to superconductivity that suggest that such order parameters would lead to a suppression of...
Show moreBSCCO2212 is a hightemperature cuprate superconductor whose microscopic behavior is currently poorly understood. In particular, it is unclear whether its order parameter is consistent with swave or dwave symmetry. It has been suggested that its order parameter might take one of several forms that are consistent with dwave behavior. We present some calculations using the manybody theory approach to superconductivity that suggest that such order parameters would lead to a suppression of the critical temperature in the presence of impurities. Because some experiments have suggested the critical temperature of BSCCO2212 is relatively independent of the concentration of impurities, this lends support to the hypothesis that its order parameter has swave symmetry.
Show less  Date Issued
 2016
 Identifier
 CFH2000073, ucf:45541
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFH2000073