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We have studied the magnetoresistance of electrodeposited Bi wires with diameters between 200 nm and 2 μm in magnetic fields up to B=55 T. In zero field, the resistance increases with decreasing temperature, indicating that the mean free path is strongly influenced by the nanowire geometry. The high-field magnetoresistance shows strong dependence on field orientation; typically 200% for B parallel to the wires, and 600%–800% for B perpendicular to the wires. The perpendicular magnetoresistance is well described by a modified two-current model which suggests that the high-field response of the arrays is fairly insensitive to the wire diameter, and is dominated by bulk properties of Bi.

We discuss Kondo insulators in the context of recent experimental results. These experiments address the questions of the relationship of spin and charge excitations, the temperature dependence of the gap, and the existence of 'failed' insulators.

We discuss Kondo insulators in the context of recent experimental results. These experiments address the questions of the relationship of spin and charge excitations, the temperature dependence of the gap, and the existence of 'failed' insulators.