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. / At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Manuscript.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:su-62583 |
| Date | January 2011 |
| Creators | Katterwe, Sven-Olof |
| Publisher | Stockholms universitet, Fysikum, Stockholm : Department of Physics, Stockholm University |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, info:eu-repo/semantics/doctoralThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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