Nature Commun. 5, 4745 (2014)

By decreasing the size of a material down to the nanometre scale, the energy levels that can be occupied by electrons are split into well-defined states. Such control of the energy levels is key for the realization of devices based on the conduction of single electrons, but is hampered by lattice vibrations that provide additional thermal energy to the electrons. Pradeep Bhadrachalam and colleagues now show that the effects of thermal excitations on electron transport can be suppressed by combining the discrete energy levels of a quantum dot with those of a quantum well. The latter material acts as a filter for the charges injected from an electrode into the quantum dot, and allows efficient collection at the second electrode only of those electrons that are not thermally excited — that is, cold electrons. A single-electron transistor based on this energy-filtering mechanism shows clear signatures of electron transport through discrete single-electron levels up to 295 K.