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Stabilization of the in-phase fluxon state by geometrical confinement in small Bi2Sr2CaCu2O8+x mesa structures
Stockholm University, Faculty of Science, Department of Physics. (Experimental Condensed Matter Physics)
Stockholm University, Faculty of Science, Department of Physics. (Experimental Condensed Matter Physics)
2009 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 80, no 2, 020502(R)- p.Article in journal (Refereed) Published
Abstract [en]

Thein-phase (rectangular) fluxon lattice is required for achieving coherent THzemission from stacked Josephson junctions. Unfortunately, it is usually unstabledue to mutual repulsion of fluxons in neighbor junctions, whichfavors the out-of-phase (triangular) lattice. Here we experimentally study magneticfield modulation of the critical current in small Bi-2212 mesastructures with different sizes. Clear Fraunhofer-like modulation is observed whenthe field is aligned parallel to CuO planes. For longmesas the periodicity of modulation is equal to half theflux quantum per intrinsic Josephson junction, corresponding to the triangularfluxon lattice. However, the periodicity is changed to one fluxquantum, characteristic for the rectangular fluxon lattice, both by decreasingthe length of the mesas and by increasing magnetic field.Thus, we demonstrate that the stationary in-phase fluxon state canbe effectively stabilized by geometrical confinement in small Bi-2212 mesastructures.

Place, publisher, year, edition, pages
2009. Vol. 80, no 2, 020502(R)- p.
Keyword [en]
bismuth compounds, calcium compounds, critical currents, flux-line lattice, high-temperature superconductors, Josephson effect, strontium compounds, terahertz waves
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-32819DOI: 10.1103/PhysRevB.80.020502ISI: 000268617500014OAI: oai:DiVA.org:su-32819DiVA: diva2:281638
Available from: 2009-12-16 Created: 2009-12-16 Last updated: 2011-09-23Bibliographically approved
In thesis
1. Properties of small Bi2Sr2CaCu2O8 intrinsic Josephson junctions: confinement, flux-flow and resonant phenomena
Open this publication in new window or tab >>Properties of small Bi2Sr2CaCu2O8 intrinsic Josephson junctions: confinement, flux-flow and resonant phenomena
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, intrinsic Josephson junctions, naturally formed in the strongly anisotropic high-temperature superconductor Bi2Sr2CaCu2O8 (Bi-2212), are studied experimentally. For this purpose, small mesa structures are fabricated on the surface of single crystals using micro- and nano-fabrication tools, focused ion beam is used to reduce the area of the mesa-structures down to ≈ 1 × 1 μm2.

The properties of charge transport across copper-oxide layers inside the mesas are studied by intrinsic tunneling spectroscopy. Temperature, bias and magnetic field dependences of current-voltage characteristics are examined.

In the main part of the thesis, the behavior of intrinsic Josephson junctions in magnetic fields B parallel to the copper-oxide planes is studied. Parallel magnetic fields penetrate the junctions in the form of Josephson vortices (fluxons). At high magnetic fields, fluxons are arranged in a regular lattice and are accelerated by a sufficient high transport current. As the fluxon lattice is moving through the mesa, it emits electromagnetic waves in the important THz frequency range. Properties of Bi-2212 mesas in this flux-flow regime are studied in this thesis.

The following new observations were made during the course of this work: a crossover from thermal activation above Tc to quantum tunneling below Tc is seen in the interlayer transport-mechanism, the Fraunhofer pattern of Ic(B) is observed clearly in Bi-2212, superluminal electromagnetic cavity resonances and phonon-polaritons are observed in Bi-2212.

It is argued that the employed technique for miniaturization of mesas and the obtained results can be useful for a better understanding of fundamental properties of high-temperature superconductors and for the realizations of coherent flux-flow oscillators and coherent phonon-polariton generators in the important THz frequency range.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2011. 105 p.
Keyword
high-temperature superconductivity, intrinsic Josephson junctions, tunneling, fluxons, flux-flow oscillator, THz-emission, cavity resonances, polaritons, micro/nano-fabrication
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-62583 (URN)978-91-7447-358-2 (ISBN)
Public defence
2011-10-27, FB41, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Manuscript. Available from: 2011-10-05 Created: 2011-09-23 Last updated: 2011-10-07Bibliographically approved

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