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Stability and chaos of a driven nanoelectromechanical 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.
2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 19, 195439- p.Article in journal (Refereed) Published
Abstract [en]

We consider the motion of and Josephson current through a mechanically oscillating superconducting island asymmetrically embedded in a Josephson junction. The electromechanical coupling is provided by distance-dependent tunneling rates between the electrodes and the island. The system asymmetry, resulting from the geometrical configuration, leads, for weak coupling, to an equation of the mechanical motion that reduces to the well-known Duffing equation. At zero bias voltage the island motion is determined by the homogenous Duffing equation that opens up two separate regions of solutions depending on the superconducting phases. The island either moves under influence of an anharmonic single-well potential or is governed by a double-well potential that allows for off-center oscillations. Under applied bias voltage the island equation of motion turns into a modified Duffing equation, with time-dependent coefficients, that demonstrate both quasiperiodic and chaotic behavior.

Place, publisher, year, edition, pages
2012. Vol. 85, no 19, 195439- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-175613DOI: 10.1103/PhysRevB.85.195439ISI: 000304173400005OAI: oai:DiVA.org:uu-175613DiVA: diva2:532853
Available from: 2012-06-12 Created: 2012-06-11 Last updated: 2017-12-07Bibliographically 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. 87 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1282
Keyword
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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