J. Keller

Thermal fluctuations in ultrasmall intrinsic Josephson junctions

Current-voltage curves of small area hysteretic intrinsic Josephson junctions, for which the Josephson energy

Superlattice with hot electron injection: An approach to a Bloch oscillator

{E}_{J}=ensuremath{Elzxh}{J}_{c}/2e

Charge-imbalance effects in intrinsic Josephson systems

is of the order of thermal energy

Theory for the coupling between longitudinal phonons and intrinsic Josephson oscillations in layered superconductors

kT,

Collective modes in the electronic polarization of double-layer systems in the superconducting state.

are investigated. A nonmonotonic temperature dependence of the switching current is observed and explained by thermal phase fluctuations. At low temperatures premature switching from the superconducting into the resistive state is the most important effect of fluctuations. At high temperatures only a single resistive branch is observed. At the cross over temperature a hysteretic phase-diffusion branch exists. It shows the importance of a frequency-dependent impedance of an external circuit formed by the leads.

Static charge coupling of intrinsic Josephson junctions

A semiconductor superlattice with hot electron injection into the miniband is considered. The injection changes the stationary distribution function and results in a qualitative change of the frequency behavior of the differential conductivity. In the regime with Bloch oscillating electrons and injection into the upper part of the miniband the region of negative differential conductivity is shifted from low frequencies to higher frequencies. We find that the dc differential conductivity can be made positive and thus the domain instability can be suppressed. At the same time the high-frequency differential conductivity is negative above the Bloch frequency. This opens another way to make a Bloch oscillator operating at THz frequencies.

Coupling of intrinsic Josephson oscillations in layered superconductors by charge fluctuations

We report on two types of experiments with intrinsic Josephson systems made from layered high-

Subgap structures in the current-voltage characteristics of the intrinsic Josephson effect due to phonons

{T}_{c}

Phonons in intrinsic Josephson systems with parallel magnetic field

superconductors which show clear evidence of nonequilibirum effects. (1) In two-point measurements of

Electron-phonon interaction in Hubbard systems

mathrm{IV}