Hot-electron spectrometry with quantum point contacts

Ballistic transport of electrons over several micrometers with excess energy of up to the order of the Fermi energy has been observed in the two-dimensional electron gas of a GaAs-${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As heterostructure. Quantum point contacts in an electron-focusing geometry have been used as a novel magnetic spectrometer to measure directly the kinetic energy of injected electrons. The observed energy gain is linear in the total applied voltage, and the slope allows a determination of the local voltage drop over the point contact.