Universal Conductance Fluctuations in Metals

The conductance of any metallic sample is predicted to fluctuate as a function of chemical potential or magnetic field by an amount of order $\frac{e^2}{h}(\simeq 4\times {10}^{-5\mathrm{}}{\Omega }^{-1\mathrm{}})$ independent of sample size and degree of disorder as long as the temperature is low enough so that $\mathrm{kT}$ and the inelastic-scattering rate are less than the inverse time to diffuse across the sample. The theory is shown to be in excellent agreement with numerical simulations and explains many features of experiments on small wires and rings.