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Accueil du site > Equipes de recherche > Systèmes Quantiques Complexes > Systèmes désordonnés - Disordered systems
Systèmes désordonnés - Disordered systems
A linear wave propagating in a thick disordered medium experiences multiple scattering events and is turned into many partial waves which interfere (speckle). At first it was thought that the corresponding amplitudes had uncorrelated phases. As a consequence, even in the absence of any phase-breaking mechanism, disorder average was expected to wash out all interference effects, meaning that transport would ultimately be described by a diffusion process. In 1958, in the context of electronic transport, Anderson proved this assumption to be wrong by evidencing a disorder-induced metal-insulator transition, i.e. the suppression of diffusive transport due to destructive interferences (strong localization). Twenty years later, the scaling hypothesis showed that transport in 1D and 2D systems always occurs in the localized regime, while in 3D a threshold had to be crossed to reach the strong localization regime (Ioffe-Regel criterion). Thus transport appears to be diffusive at spatial scales less than the so-called localization length and is suppressed at spatial scales larger than the localization length. It was also realized that, even in the diffusive regime, some interferences were still influencing transport by reducing the diffusion constant (weak localization regime). This fact can be understood by realizing that disorder average cannot break the interference associated to scattering amplitudes counter-propagating along diffusion loops. Other related macroscopic effects are the well-known universal conductance fluctuations and the coherent backscattering effect. These effects are well understood in the case of linear media but just begin to be studied in the regime of interactions.
