The threshold behavior of the transport properties of a random metal in the critical region near a metal-insulator transition is strongly affected by the measur- ing electromagnetic fields. In spite of the randomness, the electrical conductivity exhibits striking phase-coherent ef- fects due to broken symmetry, which greatly sharpen the transition compared with the predictions of effective medium theories, as previously explained for electrical conductivities. Here broken symmetry explains the sign reversal of the T - 0 magnetoconductance of the metal-insulator transition in Si(B,P), also previously not understood by effective medium theories.
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