Superconductivity is a fascinating manifestation of quantum mechanics on a macroscopic scale that has led to greater insights of the strongly correlated physics of a large number of interacting electrons ever since its discovery $\sim$ 100 years ago in elemental Hg. The unconventional superconductors that are based on uranium offer some of the most exotic behaviors uncovered to date, such as multiple superconducting phases in UPt$_3$ and ferromagnetism-mediated superconductivity in UCoGe. In this dissertation we report a new-found consequence of the broken time-reversal symmetry of the B-Phase of single-crystalline UPt$_3$. We observed effects of this broken time-reversal symmetry by using small-angle neutron scattering to investigate the structure of its vortex lattice. These results highlight a new method of investigating a time-reversal symmetry-breaking superconductor and provide evidence of a unique vortex core structure modification in UPt$_3$. The usage of a neutron beam was also discovered to cause a gradual disordering of the vortex lattice due to neutron-induced nuclear fission of $^{235}$U isotope depositing a comparatively massive amount of localized energy within the sample. This neutron induced fission drives the ordered vortex lattice towards a disordered vortex glass state over several hours and provides a novel method of studying collective vortex matter properties and the relation between ordered and disordered states of vortex matter. We have also grown single crystalline UCoGe using ultra-high vacuum electron-beam zone-refining and report on the electrical and magnetic properties of our UCoGe and compare with samples made by other methods. We have discovered an unreported metallurgical phase of U, Co, and Ge that figures prominently in the properties of UCoGe samples. Our results will enable improvement of UCoGe single-crystal sample quality, which has thus far been a hindrance to experiment on this new and unusual superconductor. We also discuss the effects of time-reversal symmetry-breaking in the thermal transport of UPt$_3$, which can result in an anomalous thermal Hall effect. The results contained in this thesis will guide future experimental and theoretical work on the exotic ground states of unconventional superconductors.

Creator

• Avers, Keenan Edward

DOI

• https://doi.org/10.21985/n2-bmey-qq19

Subject

• Materials Science
• Condensed matter physics
• Low temperature physics

Language

• en

Alternate Identifier

• etdadmin_upload_794332
• http://dissertations.umi.com/northwestern:15459

Keyword

• Crystal Growth
• Uranium Superconductors
• Unconventional Superconductors
• Time-Reversal Symmetry-Breaking
• Superconducting Vorticies
• Ferromagnetic Superconductors

Date created

• 2021-01-01

Resource type

• Dissertation

Rights statement

• In Copyright