PerspectiveApplied Physics

Ohm's Law in a Quantum World

Science  06 Jan 2012:
Vol. 335, Issue 6064, pp. 45-46
DOI: 10.1126/science.1215900

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Summary

Ohm's law is an empirical law based on the observation that the electrical transport properties of materials exhibit linear behavior. The principle is that the voltage that develops across a piece of conducting material is linearly proportional to the current flowing through it; the constant of proportionality being termed the resistance, V = IR (1). Such behavior is the backbone of classical conduction in these materials. In the 1920s and 1930s, it was expected that classical behavior would operate at macroscopic scales but would break down at the microscopic scale, where it would be replaced by the new quantum mechanics. The pointlike electron motion of the classical world would be replaced by the spread out quantum waves. These quantum waves would lead to very different behavior. On page 64 of this issue, Weber et al. (2) have constructed atomic-scale nanowires in Si and have observed that Ohm's law remains valid, even at very low temperatures, a surprising result that reveals classical behavior in the quantum regime.