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 T_c to quantum tunneling below T_c is seen in the interlayer transport-mechanism, the Fraunhofer pattern of I_c(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.

In this thesis, the tunneling between individual atomic layers in structures of Bi₂Sr₂CaCu₂O_8+x based high-temperature superconductors are experimentally studied employing the intrinsic Josephson effect. A special attention is paid on the fabrication of small mesa structures using micro and nanofabrication techniques.

Different resonant phenomena are studied in the dynamic fluxon state at high magnetic fields, including Eck-resonances and Fiske steps.

The periodic Fraunhofer-like modulation of the critical current of the junctions as a function of in-plane magnetic field is investigated. A transition from a modulation with a half flux quantum to a flux quantum periodicity is demonstrated with increasing field and decreasing junction length. It is interpreted in terms of the static fluxon lattice of stacked, strongly cou- pled intrinsic Josephson junctions and compared with theoretical predictions. A fluxon phase diagram is constructed. It is experimentally found that a stable rectangular fluxon lattice can be obtained at a flux density larger than 1.3 fluxons per Josephson penetration length and junction, Ф₀/λ_Js. Numerical simulations have been carried out to complement the experimental data.

The resistive switching of mesas at high bias is studied. It is attributed to a persistent electri- cal doping of the crystal. Superconducting properties such as the critical current and tempera- ture and the tunneling spectra are analyzed at different doping states of the same sample. The dynamics of the doping is studied, and attributed to two mechanisms; a charge-transfer effect and oxygen reordering.

In this thesis, the tunneling between individual atomic layers in structures of Bi₂Sr₂CaCu₂O_8+x based high-temperature superconductors are experimentally studied employing the intrinsic Josephson effect. A special attention is paid to the fabrication of small mesa structures using micro and nanofabrication techniques.

In the first part of the thesis, the periodic Fraunhofer-like modulation of the critical current of the junctions as a function of in-plane magnetic field is investigated. A transition from a modulation with a half flux quantum to a flux quantum periodicity is demonstrated with increasing field and decreasing junction length. It is interpreted in terms of the transformation of the static fluxon lattice of stacked, strongly coupled intrinsic Josephson junctions and compared with theoretical predictions. A fluxon phase diagram is constructed.Numerical simulations have been carried out to complement the experimental data.

In the second part of the thesis, different resonant phenomena are studied in the dynamic flux-flow state at high magnetic fields, including Eck-resonances and Fiske steps. Different resonant modes and their velocities, including superluminal modes, are identified.

In the third part, different experiments attempting to detect radiation from small mesa structures using different setups based on hot-electron bolometer mixers and calorimeters are described. No distinct radiation with emission powers higher than about 500pW could be detected. Furthermore, the interaction with external GHz-radiation is studied. Resonances attributed to an induced flux-flow are observed, and the reflectivity of the sample can be tuned by switching mesas between the superconducting and quasiparticle state.

In the last part, the resistive switching of mesas at high bias is studied. It is attributed to a persistent electrical doping of the crystal. Superconducting properties such as the critical current and temperature and the tunneling spectra are analyzed at different doping states of the same sample. The dynamics of the doping is studied, and attributed to two mechanisms; a charge-transfer effect and oxygen reordering