Electron focusing has been used byW

Electron focusing has been used byWilliamson et al.355 to study scattering processes for “hot” electrons, with an energy in excess of the Fermi energy, and for “cool” holes, or empty states in the conduction band below the Fermi level (see Ref.307 for a review). An interesting aspect of hot-electron focusing is that it allows a measurement of the local electrostatic potential drop across a current-carrying quantum point contact,355 something that is not possible using conventional resistance measurements, where the sum of electrostatic and chemical potentials is measured. The importance of such alternative techniques to study electrical conduction has been stressed by Landauer.356