THE MINIMUM METALLIC CONDUCTIVITY IN THE PRESENCE OF A STRONG MAGNETIC-FIELD

At a metal-insulator transition of Anderson type caused by a change in volume or composition in an alloy, the conductivity at the limit of low temperatures goes continuously to zero; there is no minimum metallic conductivity. Long and Pepper in 1984, however, gave theoretical reasons for expecting that a transition induced by a strong magnetic field could prove an exception and supported their conjecture by experiments on doped InP. Recently however, Biskupski, El Kaaouachi and Briggs in 1992 came to contrary conclusions also for InP. The theoretical position reviewed also by Kaveh and Mott in 1985 is reconsidered in this letter, and it is concluded that, under certain very restricted conditions, sigma(min) (almost-equal-to 0.03e2 /HBARa) can be observed, and a hypothesis for the differing results of these two groups of workers is proposed.