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Probing vortex Majorana fermions and topology in semiconductor/superconductor heterostructures
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 21, 214514Article in journal (Refereed) Published
Abstract [en]

We investigate the local density of states, spectral function, and superconducting pair amplitudes for signatures of Majorana fermions in vortex cores in ferromagnetic and spin-orbit coupled semiconductor/superconductor heterostructures. We show that the Majorana fermion quasiparticle momentum distribution is always symmetrically distributed at a finite radius around a high-symmetry point, thereby providing a necessary condition for a low-energy state to be a Majorana fermion. In real-space profiles of the local density of states through the vortex core the Majorana fermion, together with other finite-energy vortex states, forms a characteristic X-shape structure only present at nontrivial topology. Moreover, we find that the Mexican hat band structure property of the topologically nontrivial phase translates into multiple high-intensity band edges and also vortex core states located above the superconducting gap in the local density of states. Finally, we find no strong correlation between odd-frequency pairing and the appearance of Majorana fermions, but odd-frequency pairing exists as soon as ferromagnetism is present. In fact, we find that the only vortex superconducting pair amplitude directly related to any phase transition is the appearance of certain spin-triplet p-wave pairing components in the vortex core at a pre-topological vortex core widening transition.

Place, publisher, year, edition, pages
2015. Vol. 91, no 21, 214514
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-258333DOI: 10.1103/PhysRevB.91.214514ISI: 000356477400004OAI: oai:DiVA.org:uu-258333DiVA: diva2:841834
Funder
Swedish Research Council
Available from: 2015-07-15 Created: 2015-07-13 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Topological band theory and Majorana fermions: With focus on self-consistent lattice models
Open this publication in new window or tab >>Topological band theory and Majorana fermions: With focus on self-consistent lattice models
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the most central concepts in condensed matter physics is the electronic band structure. Although band theory was established more than 80 years ago, recent developments have led to new insights that are formulated in the framework of topological band theory. In this thesis a subset of topological band theory is presented, with particular focus on topological supercon- ductors and accompanying Majorana fermions. While simple models are used to introduce basic concepts, a physically more realistic model is also studied intensely in the papers. Through self- consistent tight-binding calculations it is confirmed that Majorana fermions appear in vortex cores and at wire end points when the superconductor is in the topologically non-trivial phase. Many other properties such as the topological invariant, experimental signatures in the local density of states and spectral function, unconventional and odd-frequency pairing, the precense of spin-polarized currents and spin-polarization of the Majorana fermions, and a local π-phase shift in the order parameter at magnetic impurities are also investigated. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 144 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1441
Keyword
Topology, Majorana, superconductivity, material physics, numerical calculations, tight-binding, mean-field
National Category
Condensed Matter Physics Physical Sciences
Identifiers
urn:nbn:se:uu:diva-305212 (URN)978-91-554-9728-6 (ISBN)
Public defence
2016-12-09, Häggsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2016-11-15 Created: 2016-10-12 Last updated: 2016-11-23

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Björnson, KristoferBlack-Schaffer, Annica M.

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