Spin-Mediated Transport in Superconducting and Spin-Polarized Systems
The effects of spin-imbalance on the electronic transport properties of spin-polarized and superconducting systems have been studied in detail. The transport properties of the quaternary Heusler alloys Co2MnSi1-xAlx (0≤x≤1), which have been theoretically predicted to develop a half-metallic band str...
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ndltd-LSU-oai-etd.lsu.edu-etd-11102014-1553042014-11-18T03:44:24Z Spin-Mediated Transport in Superconducting and Spin-Polarized Systems Prestigiacomo, Joseph C. Physics & Astrononomy The effects of spin-imbalance on the electronic transport properties of spin-polarized and superconducting systems have been studied in detail. The transport properties of the quaternary Heusler alloys Co2MnSi1-xAlx (0≤x≤1), which have been theoretically predicted to develop a half-metallic band structure as x→0, were investigated. Resistivity versus temperature measurements as a function of Al concentration (x) revealed a systematic reduction in the residual resistivity ratio as well as a transition from weakly-localized to half-metallic conduction as x→0. From measurements of the ordinary and anomalous Hall effects, the charge carrier concentration was found to increase, while the anomalous Hall coefficient decreased by nearly an order of magnitude with each sample as x→0 (∆x=0.25). Scaling of the anomalous Hall effect with longitudinal resistivity reveals that both the skew-scattering and intrinsic contributions grow quickly as x→1, indicating that disorder and band-structure effects cause the large anomalous Hall effect magnitudes observed for Co2MnAl. The non-equilibrium behavior of disordered superconducting Al films in high Zeeman fields has also been investigated. The tunneling density-of-states of the films were measured through the first-order Zeeman critical field transition. It is found that films with sheet resistances of a few hundred ohms exhibit large avalanche-like collapses of the condensate on the super-heating branch of the critical field hysteresis loop. In contrast, the transition back into the superconducting phase (i.e., along the super-cooling branch) is always continuous. These avalanches are suppressed by tilting the field as little as 1.5° and disappear above T = 300 mK, although the transition remains hysteretic. The fact that the condensate follows an unstable trajectory to the normal state suggests that the order-parameter in the hysteretic regime is not homogeneous. It is argued that this unusual behavior is a manifestation of the disordered Larkin-Ovchinnikov phase, which is a disordered remnant of the elusive, spin-imbalanced superconducting state known as the Fulde-Ferrell-Larkin-Ovchinnikov phase. Butler, Les Lee, Hwang Sheehy, Daniel Stadler, Shane Adams, Philip LSU 2014-11-17 text application/pdf http://etd.lsu.edu/docs/available/etd-11102014-155304/ http://etd.lsu.edu/docs/available/etd-11102014-155304/ en restricted I hereby certify that, if appropriate, I have obtained and attached herein a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to LSU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below and in appropriate University policies, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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Physics & Astrononomy Prestigiacomo, Joseph C. Spin-Mediated Transport in Superconducting and Spin-Polarized Systems |
description |
The effects of spin-imbalance on the electronic transport properties of spin-polarized and superconducting systems have been studied in detail. The transport properties of the quaternary Heusler alloys Co2MnSi1-xAlx (0≤x≤1), which have been theoretically predicted to develop a half-metallic band structure as x→0, were investigated. Resistivity versus temperature measurements as a function of Al concentration (x) revealed a systematic reduction in the residual resistivity ratio as well as a transition from weakly-localized to half-metallic conduction as x→0. From measurements of the ordinary and anomalous Hall effects, the charge carrier concentration was found to increase, while the anomalous Hall coefficient decreased by nearly an order of magnitude with each sample as x→0 (∆x=0.25). Scaling of the anomalous Hall effect with longitudinal resistivity reveals that both the skew-scattering and intrinsic contributions grow quickly as x→1, indicating that disorder and band-structure effects cause the large anomalous Hall effect magnitudes observed for Co2MnAl.
The non-equilibrium behavior of disordered superconducting Al films in high Zeeman fields has also been investigated. The tunneling density-of-states of the films were measured through the first-order Zeeman critical field transition. It is found that films with sheet resistances of a few hundred ohms exhibit large avalanche-like collapses of the condensate on the super-heating branch of the critical field hysteresis loop. In contrast, the transition back into the superconducting phase (i.e., along the super-cooling branch) is always continuous. These avalanches are suppressed by tilting the field as little as 1.5° and disappear above T = 300 mK, although the transition remains hysteretic. The fact that the condensate follows an unstable trajectory to the normal state suggests that the order-parameter in the hysteretic regime is not homogeneous. It is argued that this unusual behavior is a manifestation of the disordered Larkin-Ovchinnikov phase, which is a disordered remnant of the elusive, spin-imbalanced superconducting state known as the Fulde-Ferrell-Larkin-Ovchinnikov phase. |
author2 |
Butler, Les |
author_facet |
Butler, Les Prestigiacomo, Joseph C. |
author |
Prestigiacomo, Joseph C. |
author_sort |
Prestigiacomo, Joseph C. |
title |
Spin-Mediated Transport in Superconducting and Spin-Polarized Systems |
title_short |
Spin-Mediated Transport in Superconducting and Spin-Polarized Systems |
title_full |
Spin-Mediated Transport in Superconducting and Spin-Polarized Systems |
title_fullStr |
Spin-Mediated Transport in Superconducting and Spin-Polarized Systems |
title_full_unstemmed |
Spin-Mediated Transport in Superconducting and Spin-Polarized Systems |
title_sort |
spin-mediated transport in superconducting and spin-polarized systems |
publisher |
LSU |
publishDate |
2014 |
url |
http://etd.lsu.edu/docs/available/etd-11102014-155304/ |
work_keys_str_mv |
AT prestigiacomojosephc spinmediatedtransportinsuperconductingandspinpolarizedsystems |
_version_ |
1716719667434749952 |