Thesis (doctoral)--Helsinki University of Technology, 2004. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (doctoral)--Technische Universiteit Delft, 2002. / Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 300-311).

This thesis details recent work on an innovative new approach to Josephson junction fabrication. These junctions are created in low TC superconductor-normal metal bilayer tracks on a deep submicron scale using a Focused Ion Beam Microscope (FIB). The FIB is used to mill away a trench 50_nm wide in the upper layer of niobium superconductor (125 nm thick), weakening the superconducting coupling and resulting in a Josephson junction. With the aid of a newly developed in situ resistance measurement technique it is possible to determine the cut depth to a high degree of accuracy and hence gain insight into how this affects the resulting device parameters. Devices fabricated over a wide range of cut depths and copper normal metal layer thicknesses (0-175 nm) have been thoroughly characterized at 4.2 K in terms of current-voltage (I-V) characteristics, magnetic field- and microwave-response. In selected cases I-V characteristics have been studied over the full temperature range from TC down to 300 mK. Devices with resistively-shunted (RSJ) I-V characteristics and ICRN products above 50 μV at 4.2 K have been fabricated reproducibly. This work has been complemented by Transmission Electron Microscopy (TEM) studies that have allowed the microstructure of the individual devices to be inspected and confirm the validity of the in situ resistance measurement. The individual junction devices are promising candidates for use in the next generation of Josephson voltage standards. In collaboration with Dr. Sam Benz at the National Institute of Standards and Technology (NIST) in the U.S., series arrays of junctions have been fabricated and characterized. Phase-locking behaviour has been observed in arrays of 10 junctions of spacings 0.2 to 1.6 μm between 4.2 K and TC in spite of the relatively large spread in individual critical currents. Strategies for minimizing junction parameter spread and producing large-scale arrays are discussed. The opportunities offered by the FIB for the creation of novel device structures has not been overlooked. By milling a circular trench in the Nb Cu bilayer a Corbino geometry SNS junction is created. In this unique device the junction barrier is enclosed in a superconducting loop, implying that magnetic flux can only enter the barrier as quantized vorticies. This gives rise to a startling magnetic field response - with the entry of a vortex the critical current is suppressed from its maximum value to zero. Experimental results and theoretical modeling are reported. Possible future applications of this novel device geometry (which may be of relevance to Quantum Computing and to studies of Berry's phase effects) are considered.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

A model for the Josephson junction is constructed based on two macroscopic angular momentum vectors. These vectors, which interact via a Heisenberg-like Hamiltonian, are defined using Anderson's pseudospin concept in superconductivity. Along with this, a new state vector, which affords a more complete description of the constant-charge-imbalance mode of the junction, is explicitly constructed. The resulting equations of motion lead directly to the basic Josephson results and at the same time provide a simple physical picture for the dynamical behavior of the junction. Both the Anderson (n,(phi)) and Feynman two-state models of the junction are shown to be equivalent to a restricted form of the angular momentum approach. The process of formulating the junction problem in terms of pseudo-angular-momentum together with the above identification constitutes a microscopic derivation of the Feynman method. A perturbation theory calculation is carried out within the full pseudo-angular-momentum equations of motion to determine how this approach differs from the earlier ones.

No description available.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 100-102).

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published_or_final_version / abstract / toc / Physics / Doctoral / Doctor of Philosophy