Properties of small Bi2Sr2CaCu2O8 intrinsic Josephson junctions: confinement, flux-flow and resonant phenomena
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
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.
high-temperature superconductivity, intrinsic Josephson junctions, tunneling, fluxons, flux-flow oscillator, THz-emission, cavity resonances, polaritons, micro/nano-fabrication
Condensed Matter Physics
Research subject Physics
IdentifiersURN: urn:nbn:se:su:diva-62583ISBN: 978-91-7447-358-2OAI: oai:DiVA.org:su-62583DiVA: diva2:443129
2011-10-27, FB41, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Ustinov, Alexey, Professor
Krasnov, Vladimir M., Professor
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Manuscript.
List of papers