Resistance in Superconducting Epitaxial Niobium Nanowires

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• McArdle, Timothy James

Contributors dc:contributor

• Berzryadin, Alexey

• Physics, Condensed Matter

Language dc:language

eng

Identifier

(MiAaPQ)AAI3392211

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/80615