Ph. D. Thesis: Properties of small Bi2Sr2CaCu2O8 intrinsic Josephson junctions: confinement, flux-flow and resonant phenomena
by
Sven-Olof Katterwe(Stockholm University, Department of Physics)
→
Europe/Stockholm
FB41
FB41
Description
In this thesis, intrinsic Josephson junctions, naturally formed in the strongly anisotropic hightemperature
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 currentvoltage
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.
