Single-Channel Transport in Disordered Multichannel Systems
Mercredi 7 septembre 2011
à 11h en salle C. Brot
Electronic transport in conductors or light or sound in samples in which randomly scattered waves diffuse may be characterized by the transmittance, T, which is equal to the number of effective open channels, Neff, with transmission coefficients close to unity. Beyond the localization length ξ , at which T= Neff =1, T becomes dominated by a single channel of the largest transmission which falls exponentially with length L due to Anderson localization. Here the crossover to single-channel transport in disordered multichannel systems is observed in statistics measurements of microwave radiation transmitted in ensembles of quasi-one-dimensional (Q-1D) random waveguides. The degree of fluctuations in transmitted, “speckle” intensity relative to transmittance fluctuations exhibits a universal scaling behavior in the crossover to the single-channel regime, in which the disordered system can be treated as a 1D localized system coupled diffusely through all independent channels to the surrounding medium. We also observe single-channel pulse transmission in localized Q-1D waveguides at short and long time delays following a pulsed excitation. This indicates that localized eigenmodes of a multichannel disordered system, including rare-occurred, short-lived “necklace” states occupy distinct transmission eigenchannels of the system.
Voir en ligne : University of Texas, San Antonio
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