Electrical pulse measurement, inelastic relaxation, and non-equilibrium transportin a quantum dot

Abstract

We review electrical pulse experiments carried out to probe inelastic energyrelaxation processes and related non-equilibrium transport characteristicsof quantum dots (QDs) in the Coulomb blockade (CB) regime. Incontrast to the relatively short momentum relaxation time (∼10ns) that can be understood on the basis of acoustic phonon emission, the spin-fliprelaxation time is found to be extremely long (∼200 µs).The spin relaxation process in our QDs is actually dominated by a cotunnellingprocess, and thus the intrinsic spin relaxation should have a longer relaxationtime. The long relaxation time is discussed in terms of potential applications tospin-based quantum information storage. On the other hand, the extremely longspin relaxation process can induce considerable fluctuation of the spin, charge,and total energy of the QD. The absence of efficient spin relaxation processes cancause highly non-equilibrium transport, which actually ‘breaks down’ thesingle-electron tunnelling scheme. The non-equilibrium effects must beconsidered when electrons and spins are manipulated in the CB regime.