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dc.contributor.authorSprau, Peter Oliver
dc.date.accessioned2018-04-26T14:16:04Z
dc.date.available2018-04-26T14:16:04Z
dc.date.issued2017-08-30
dc.identifier.otherSprau_cornellgrad_0058F_10323
dc.identifier.otherhttp://dissertations.umi.com/cornellgrad:10323
dc.identifier.otherbibid: 10361432
dc.identifier.urihttps://hdl.handle.net/1813/56771
dc.description.abstractFeSe is the focus of intense research interest because of its unusual non-magnetic nematic state and because it forms the basis for achieving the highest critical temperatures of any iron-based superconductor. However, its Cooper pairing mechanism has not been determined because an accurate knowledge of the momentum-space structure of superconducting energy gaps $\Delta_i(\vec{k})$ on the different electron-bands $E_i(\vec{k})$ does not exist. Here we use Bogoliubov quasiparticle interference (BQPI) imaging to determine the coherent Fermi surface geometry of the $\alpha$- and $\varepsilon$-bands surrounding the $\Gamma = (0, 0)$ and $X = (\pi / a_{Fe}, 0)$ points of FeSe, and to measure their superconducting energy gaps $\Delta_{\alpha}(\vec{k})$ and $\Delta_{\varepsilon}(\vec{k})$. We show directly that both gaps are extremely anisotropic but nodeless, and are aligned along orthogonal crystal axes. Moreover, by implementing a novel technique we demonstrate the sign change between $\Delta_{\alpha}(\vec{k})$ and $\Delta_{\varepsilon}(\vec{k})$. This complex configuration of $\Delta_{\alpha}(\vec{k})$ and $\Delta_{\varepsilon}(\vec{k})$, which was unanticipated within pairing theories for FeSe, reveals a unique form of superconductivity based on orbital selective Cooper pairing of electrons from the $d_{yz}$ orbitals of iron atoms. This new paradigm of orbital selectivity may be pivotal to understanding the microscopic interplay of quantum paramagnetism, nematicity and high temperature superconductivity.
dc.language.isoen_US
dc.subjectsuperconductivity
dc.subjectCondensed matter physics
dc.subjectFeSe
dc.subjectorbital selectivity
dc.subjectScanning Tunneling Microscopy
dc.subjectstrong correlations
dc.titleDiscovery of Orbital Selective Cooper Pairing in FeSe
dc.typedissertation or thesis
thesis.degree.disciplinePhysics
thesis.degree.grantorCornell University
thesis.degree.levelDoctor of Philosophy
thesis.degree.namePh. D., Physics
dc.contributor.chairDavis, James C.
dc.contributor.committeeMemberMcEuen, Paul L.
dc.contributor.committeeMemberKim, Eun-Ah
dcterms.licensehttps://hdl.handle.net/1813/59810
dc.identifier.doihttps://doi.org/10.7298/X4TB153Z


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