We present an advanced undergraduate experiment on weak localization in thin silver films with a thickness between 60-200 angstrom, a mesoscopic length scale. At low temperatures, the inelastic dephasing length for electrons exceeds the film thickness, and the film becomes quasi-two-dimensional. In this limit, theory predicts corrections to the Drude conductivity due to the coherent interference between the wave functions of the conducting electrons, a macroscopically observable effect known as weak localization. This correction can be destroyed by the application of a magnetic field, and the resulting magnetoresistance curve provides information about electron transport in the film. (c) 2005 American Association of Physics Teachers.
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