Probing the superconducting order parameter of Iron-based superconductors through the Josephson effect

We report the results we obtained regarding the use of the Josephson effect to probe the symmetry of the superconducting order parameter of Co-doped Ba(FeAs)2 crystals (Ba122). This measurements were carried out to test the validity of the s± model, which predicts the pairing in the multiband Ba122 compounds being mediated by the exchange of spin excitations, with the condition that the electron and hole bands in the superconductor's Fermi surface have opposite signs. Josephson interferometry applied using Pb/Cu/Ba122 SNS structures in corner/edge junction configurations shows two distinct Ic patterns that support an anisotropic s-wave superconducting gap. The use of IcRN data favors the hypothesis of the gap anisotropy being in direct connection to an electron gap having an opposite sign when compared to the hole gaps in the material. Finally we considered the prediction of proximity-induced changes in the density of states of a thin film of a conventional superconductor due to the presence of a Ba122 crystal. Our results found evidence of both a positive and a negative proximity effect, which in conjunction with other features identified in the density of states spectrum of the thin film of conventional superconductor, points strongly towards the legitimacy of s± model.

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

• Atkinson Mora, Juan

Contributors dc:contributor

• Van Harlingen, Dale J.
• Giannetta, Russell W.
• Phillips, Philip W.
• Pitts, Kevin T.

• proximity effect
• Josephson
• pairing symmetry
• Ba122
• Fe-based superconductor
• Superconductor

Statement dc:rights

• Copyright 2015 Juan Miguel Atkinson Mora

Handle dc:identifier

http://hdl.handle.net/2142/78286

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/78286