Two heavy Fermion superconducting compounds, URu₂Si₂ and PuRhIn₅, were investigated by the techniques of chemical substitution and application of high magnetic fields. These materials are particularity interesting for their unique electronic and ordered state behavior (hidden order and superconducting phases) and proximity to magnetism. It is thought the superconductivity of these materials is unconventional and that they exhibit some features that are associated with quantum criticality, especially for PuRhIn₅. In earlier work URu₂Si₂ was doped with the non-isoelectric element phosphorus to produce the doping series URu₂Si₂₋ₓPₓ. During the current study, single crystals of the series were placed in high pulsed magnetic fields (up to 65T) and the evolution of the field induced phases was observed. The parent compound exhibits five unique phases in field as does the doped series up to approximately x=0.3. At this concentration and at zero field the hidden order phase is destroyed and any higher doping exhibit no ordered ground state. Over this x-range there is only one field induced state. Further increasing x (x > 0.26) pushes the system into an antiferromagnetic ground state, which has some high field ordering but at a higher magnetic fields than the lower doped compounds. This behavior is similar to the effect of Co, Rh and Ir substitution, which are also non-isoelectronic dopants that add electrons. This is in contrast to isoelectric doping (using Fe or Os) in which produce effects in the material similar to applied pressure. From this, it appears that the effects of non-isoelectric dopants might be attributed to band filling. The hidden order state of the parent compound URu₂Si₂ was also investigated with an optical magnetostriction technique in high magnetic fields. A transition from a quadratic to linear field response is seen in the signal while still in the hidden order state. This behavior is unusual and possible explanations include partial polarization of the Fermi surface and quadrupolar interactions. The Pu based superconductor PuRhIn₅ was doped with Cd and placed in high magnetic fields. Pu is both a radiological and toxicity hazard. As a result, a significant part of this project was spent controlling these hazards while enabling measurements. The phase diagram of PuRh(In₁₋ₓCdₓ)₅ in the T-x-H phase diagram was mapped and the optical magnetostriction technique was applied to the parent compound. From this data the electronic Grüneisen ratio was determined. Applying scaling arguments it was shown that the Grüneisen data is consistent with proximity to a quantum critical point, which is though to figure heavily in unconventional superconducting systems. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2018. / April 10, 2018. / Includes bibliographical references. / Greg Boebinger, Professor Directing Dissertation; Theo Siegrist, University Representative; Ross McDonald, Committee Member; Ryan Baumbach, Committee Member; Vladimir Dobrosavljevic, Committee Member; Jianming Cao, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_653527 |
| Contributors | Wartenbe, Mark (author), Boebinger, Gregory S. (professor directing dissertation), Siegrist, Theo (university representative), McDonald, Ross (committee member), Baumbach, Ryan E. (committee member), Dobrosavljević, Vladimir (committee member), Cao, Jianming (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Physics (degree granting departmentdgg) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text, doctoral thesis |
| Format | 1 online resource (97 pages), computer, application/pdf |
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