Abstract
Using nanofabrication techniques we made Si point contacts with constriction sizes down to 85 nm and investigated their I—V curves at temperatures between 300 K and 200 mK. At room temperature the devices are ohmic and obey the Maxwell resistance. Below 40 K the type of conduction at low electric fields is Mott-variable range hopping. At higher fields an intriguing non-ohmic behaviour was found which is related to formation of a spherical region of non-ohmic hopping conduction, centred around the constriction of the point contact. In this regime, the voltage at the electrodes is shown to vary as V( I) = I c R M(2( I/ I c) 1/2 −1), which is specific for the point contact geometry.
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