No abstract

In recent years, there has been interest in devices created on InGaAs due to the possibility of its use for spintronics. Nonetheless, this material is known for usually presenting some levels of disorder. We have used scanning gate microscopy to study the local potential for an in-plane gated InGaAs quantum point contact and succeeded in obtaining images corresponding to sites where same quantum interference conditions are maintained. Furthermore, we have visualized images of the local potential variations within the confined region near pinch-off condition.

Visualization of quantum interference patterns has been obtained within a quantum point contact using scanning gate microscopy. The area distribution of the interference pattern is shown to be consistent with the interference area obtained from the magnetoconductance fluctuations of a quantum point contact. Both distributions follow the Gaussian unitary ensemble, corresponding to chaotic behavior. The interference is caused by the random potential fluctuations within the channel, which is modified by the tip-induced potential.

Abstract. Two types of quantum point contacts have been studied by low temperature scanning gate microscopy. In addition to the usual bright spot, which corresponds to a large conductance change at the constriction, ring structures are observed near the center of the quantum point contact. The ring diameter shrinks with increasing base conductance when the side gate voltage is changed. The rings are thought to relate to the observation of impurity potentials in the constriction region.

The collective motion of self-driven particles shows interesting novel phenomena such as swarming and the emergence of patterns. We have recently proposed a model for counterflowing particles that captures this idea and exhibits clogging transitions. This model is based on a generalization of the Fermi-Dirac statistics wherein the maximal occupation of a cell is used. Here we present a detailed study comparing synchronous and asynchronous stochastic dynamics within this model. We show that an asynchronous updating scheme supports the mobile-clogging transition and eliminates some mobility anomalies that are present in synchronous Monte Carlo simulations. Moreover, we show that this transition is dependent upon its initial conditions. Although the Gini coefficient was originally used to model wealth inequalities, we show that it is also efficient for studying the mobile-clogging transition. Finally, we compare our stochastic simulation with direct numerical integration of partial differential equations used to describe this model.