Quantum Limit
When a conductor has spatial dimensions close to, where is Fermi wavevector of the conducting material, Ohm's law does not hold anymore. These small devices are called quantum point contacts. Their conductance must be an integer multiple of the value, where is the electronic charge and is Planck's constant. Quantum point contacts behave more like waveguides than the classical wires of everyday life and may be described by the Landauer scattering formalism. Point-contact tunneling is an important technique for characterizing superconductors.
Read more about this topic: Contact Resistance
Famous quotes containing the words quantum and/or limit:
“The receipt to make a speaker, and an applauded one too, is short and easy.—Take of common sense quantum sufficit, add a little application to the rules and orders of the House, throw obvious thoughts in a new light, and make up the whole with a large quantity of purity, correctness, and elegancy of style.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
“Today one does not hear much about him.... The fame of his likes circulates briskly but soon grows heavy and stale; and as for history it will limit his life story to the dash between two dates.”
—Vladimir Nabokov (1899–1977)