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Spin inelastic electron tunneling spectroscopy on local magnetic moment embedded in Josephson junction
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.
2014 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 108, no 6, article id 67009Article in journal (Refereed) Published
Abstract [en]

Recent experimental conductance measurements performed on paramagnetic molecular adsorbates on a superconducting surface, using superconducting scanning tunneling microscopy techniques, are theoretically investigated. For low temperatures, we demonstrate that tunneling current assisted excitations of the local magnetic moment cannot occur for voltage biases smaller than the superconducting gap of the scanning tunneling microscope. The magnetic moment is only excited for voltages corresponding to the sum of the superconducting gap and the spin excitation energies. In excellent agreement with experiment, we show that pumping into higher excitations gives additional current signatures by accumulation of density in the lower ones. Using external magnetic fields, we Zeeman-split the possible degeneracy and thereby resolve all excitations comprised in the magnetic moment.

Place, publisher, year, edition, pages
2014. Vol. 108, no 6, article id 67009
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-245544DOI: 10.1209/0295-5075/108/67009ISI: 000348204400021OAI: oai:DiVA.org:uu-245544DiVA, id: diva2:793869
Available from: 2015-03-09 Created: 2015-02-26 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Elastic and inelastic scattering effects in conductance measurements at the nanoscale: A theoretical treatise
Open this publication in new window or tab >>Elastic and inelastic scattering effects in conductance measurements at the nanoscale: A theoretical treatise
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Elastic and inelastic interactions are studied in tunnel junctions of a superconducting nanoelectromechanical setup and in response to resent experimental superconducting scanning tunneling microscope findings on a paramagnetic molecule. In addition, the electron density of molecular graphene is modeled by a scattering theory approach in very good agreement with experiment. All studies where conducted through the use of model Hamiltonians and a Green function formalism. The nanoelectromechanical system comprise two fixed superconducting leads in-between which a cantilever suspended superconducting island oscillates in an asymmetric fashion with respect to both fixed leads. The Josephson current is found to modulate the island motion which in turn affects the current, such that parameter regions of periodic, quasi periodic and chaotic behavior arise. Our modeled STM setup reproduces the experimentally obtained spin excitations of the paramagnetic molecule and we show a probable cause for the increased uniaxial anisotropy observed when closing the gap distance of tip and substrate. A wider parameter space is also investigated including effects of external magnetic fields, temperature and transverse anisotropy. Molecular graphene turns out to be well described by our adopted scattering theory, producing results that are in good agreement with experiment. Several point like scattering centers are therefore well suited to describe a continuously decaying potential and effects of impurities are easily calculated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. p. 87
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1282
Keywords
Scattering theory, Scanning tunneling microscopy, tunnel junctions, molecular graphene, paramagnetic molecules, spin interaction, nano electromechanical system, Josephson junction, superconductivity, chaos
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-261609 (URN)978-91-554-9321-9 (ISBN)
Public defence
2015-10-16, Häggsalen, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2015-09-25 Created: 2015-09-02 Last updated: 2015-10-01

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Berggren, PeterFransson, Jonas

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