A new transport phenomenon in nanostructures: a mesoscopic analog of the Braess paradox encountered in road networks

Two-parameter landscape of transport efficiency in mesoscopic networks: transitions from the Braess to normal regimes without a congestion relaxation

This paper deals with the Braess paradox in quantum transport. The scattering matrix formalism is used to consider a two-parameter family of mesoscopic conductors with the topology of the classical Braess transport network. The study investigates the mutual influence of the congestion and smoothness of the system on the Braess behavior. Both the Braess paradox and normal transport regimes coexist within the two-parametric landscape under the same congestion.

On the origins of transport inefficiencies in mesoscopic networks

A counter-intuitive behavior analogous to the Braess paradox is encountered in a two-terminal mesoscopic network patterned in a two-dimensional electron system (2DES). Decreasing locally the electron density of one channel of the network paradoxically leads to an increased network electrical conductance. Our low temperature scanning gate microscopy experiments reveal different occurrences of such puzzling conductance variations, thanks to tip-induced localized modifications of electron flow throughout the network’s channels in the ballistic and coherent regime of transport. The robustness of the puzzling behavior is inspected by varying the global 2DES density, magnetic field and the tip-surface distance. Depending on the overall 2DES density, we show that either Coulomb Blockade resonances due to disorder-induced localized states or Fabry-Perot interferences tuned by the tip-induced electrostatic perturbation are at the origin of transport inefficiencies in the network, which are lifted when gradually closing one channel of the network with the tip.