R. Richter

Critical Dynamics near the Onset of Spontaneous Oscillations in p-Germanium

The electrical avalanche breakdown of p-doped germanium at low temperatures displays self-generated current oscillations. The investigation of the transition from a stable fixed point to a limit cycle yields a scaling behaviour known from the saddle node bifurcation on a limit cycle.

Evidence of Type-III Intermittency in the Electric Breakdown of p-Type Germanium

Electric oscillations arising spontaneously in the low-temperature avalanche breakdown of p-germanium are investigated with respect to the intermittent routes to chaos. The experimental data display several universal features of type-III intermittency.

Delayed Feedback Control of Chaos in an Electronic Double-Scroll Oscillator

Abstract We present experimental results on stabilizing unstable periodic orbits of an autonomous chaos oscillator based on a simple electronic circuit. Control is achieved by applying the difference between the actual and a delayed output signal of the oscillator. The quality of chaos control can be measured via the strength of perturbation. The dependence on the delay time shows a characteristic resonance-type behavior.

Spatio — Temporal Correlations in Semiconductors

The electric avalanche breakdown of homogeneously doped semiconductors at low temperatures can be regarded as a nonequilibrium phase transition. If this breakdown is associated with negative differential conductivity, i.e. bistabihty between a low and a high conducting phase, spontaneous structure formation occurs. Current filaments as spatial structures and spontaneous oscillations as temporal structures were observed. Both structures are in close connection to each other. At the very onset of the breakdown, no stable filament can be created. Here, a firing mode of filaments was observed which displays critical dynamics like 1/f noise. The analogy to the self-organized criticality is discussed. In the breakdown regime with sufficient power dissipation, stable filaments were observed. These filaments may display low-dimensional nonlinear dynamics due to small structural changes like a breathing mode. Evidence is presented that typical nonlinear dynamics like quasiperiodicity and chaos is due to the nonlinear interaction of spatially localized oscillation centers.

Whispering Gallery Orbits in the Bunimovich Stadium

Abstract A new visualization method is found for investigating the complex ray dynamics of whispering gallery orbits inside the Bunimovich stadium. Regarding the whispering gallery as mirror cabinet, a fractal system of virtual images of the mirror walls is found which reflects the sensitive dependence of the dynamic behavior on the initial conditions.

Stochastic resonance in experiment

Abstract We observe the phenomenon of stochastic resonance in a semiconductor experiment. Originally, such an effect was predicted for bistable dynamical systems that are influenced by a periodic modulation as well as a random perturbation. In that case, a resonance peak can be observed in the power spectrum. The phenomenon investigated is the low-temperature impact ionization breakdown. There, bistability results from the competing states of low and high conductance.

On the Scaling of Type-1 Intermittency in a Semiconductor Experiment

Abstract Spontaneous oscillations developing during low-temperature impact ionization breakdown in extrinsic germanium are looked at with respect to characteristic features of type-I intermittency

Symbolic-dynamical analysis of a transition between different limit cycles observed in a semiconductor experiment

Abstract Low-temperature semiconductor impact ionization breakdown typically exhibits spontaneous current oscillations depending sensitively upon external control parameters. Discrete characteristics of the time series are transformed into a symbolic sequence. We determine the information entropies together with the order of the Markov process underlying the dynamics. These quantities allow one to characterize various transitions between different attractors in a quantitative way.

Logarithmic frequency scaling of semiconductor oscillations caused by a modified saddle-node bifurcation on a limit cycle

The oscillatory behavior of low-temperature impact ionization breakdown inp-type germanium is investigated experimentally. We explain the anomalous scaling behavior of a saddle-node bifurcation on a limit cycle in terms of a simple model approach. It represents the low-dimensional analog to a new type of intermittency proposed recently.

An oscillation mechanism of semiconductor breakdown due to magnetic field induced transverse motion of current filaments

The self-generated formation of spontaneous current oscillations developing during low-temperature impact ionization breakdown of slightly doped p-type germanium is explained, taking advantage of a model experiment. Upon applying a relatively small transverse magnetic field, the spatially inhomogeneous current distribution, manifest in the form of individual high conducting current filaments, undergoes distinct travelling dynamics that is oriented perpendicular to the direction of the electric and the magnetic field (i.e. not coincident with the direction of the current flow). The resulting magnetic field induced oscillatory behaviour can be described qualitatively by simple model considerations.