Weak localization

The weak location ( weak localization ) denotes a quantum effect in the conductivity of the electric current and generally in the scattering of waves in disordered media, causes the propagation of the waves is reduced and they are "localized".

The conductivity of an electrical conductor with an impurity as scattering centers which are responsible for the electrical resistance, can be treated classically, in principle, as long as the mean free path of the impurity in the crystal is greater than the wavelength of the electron ( for defining see Fermi pulse ). The electrons move in a straight line and are deflected to the impurity, where the phases of the different paths cancel out in the middle and so justify the classical treatment. In the quantum mechanical treatment of the case of the coherent backscattering occurs (coherent backscattering ). When an electron is scattered on a path that returns it to its starting point, then go through the same path with the same probability amplitude in the reverse direction an electron, with the contributions of the two paths, who are the same length, the same phase add (see also Cooperon diagram). For the backscattering results in a factor of two higher probability than in the classical treatment. These changes correspond to measurements in an abnormally increased resistance and was observed in the 1970s on thin films.

In the 1980s, this phenomenon was also observed in the scattering of coherent light (laser ) to colloidal suspensions ( eg, very small plastic beads in a liquid) directly and then in other wave phenomena ( even with earthquake waves. )

The phenomenon of weak localization is considered the precursor of the strong or Anderson localization in disordered media, in which the concentration of defects is so high, the whole remains under the diffusive propagation of the waves.