Eddy Current Method for Low Temperature Resistivity Measurements

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Abstract
A modified mutual inductance bridge incorporating a commercial phase‐lock amplifier has been used to measure low temperature bulk resistivities in the range from 1 to 10 000 nΩ cm. No electrical contact is required with the spherical metal samples, so that possible heat leakage along electrical leads is eliminated, and measurements can be made below 40 mdeg Kelvin using a dilution refrigerator. The bridge circuit, capable of determining resistivity changes with a precision of better than 0.3%, is described.