Resistance in Superconducting Epitaxial Niobium Nanowires
McArdle, Timothy James
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https://hdl.handle.net/2142/80615
Description
Title
Resistance in Superconducting Epitaxial Niobium Nanowires
Author(s)
McArdle, Timothy James
Issue Date
2009
Doctoral Committee Chair(s)
Berzryadin, Alexey
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Language
eng
Abstract
The thermally activated phase slip description of resistance in one-dimensional superconducting wires is unable to explain additional resistance observed in extremely narrow nanowires well below the critical temperature. However, attributing this additional resistance to quantum phase slips has been controversial. In part, this controversy is due to the amorphous nature of the majority of manufactured nanowires; such wires unavoidably contain grain-boundaries and other weak links which may contribute to or even dominate additional observed resistance. In the course of my thesis research, I have fabricated quasi one-dimensional nanowires of uniform cross-section using electron beam lithography and reactive ion etching. These nanowires are fabricated from single-crystal niobium films grown by ultra-high vacuum molecular beam epitaxy. Since the resulting wires are single-crystal and homogenous, the role of disorder is reduced and neither weak links nor grain boundaries dominate the observed DC resistance at low temperature. The epitaxial films in this study are between 10 and 30 mn thick. While the finished wires range in length from 1 to 10 mum; and in width from 35 to 400 nm. Transport measurements on the nanowires of varying widths show a range of distinct temperature dependencies below the critical temperature that cannot be accounted for by the single exponential form of the thermally activated phase slip model. The fabrication process I have developed has also recently been employed in work integrating our epitaxial niobium nanowires into microwave resonators to probe for phase fluctuations at high frequency, and into Dayem bridge DC SQUIDS designed to have sensitivity down to a single spin.
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