Spectroscopy of Equilibrium and Non-Equilibrium Charge Transfer in   Semiconductor Quantum Structures
  We investigate equilibrium and non-equilibrium charge-transfer processes by performing high-resolution transport spectroscopy. Using electrostatically defined quantum dots for energy-selective emission and detection, we achieved unprecedented spectral resolution and a high degree of tunability of relevant experimental parameters. Most importantly, we observe that the spectral width of elastically transferred electrons can be substantially smaller than the linewidth of a thermally broadened Coulomb peak. This finding indicates that the charge-transfer process is fast compared to the electron--phonon interaction time. By drawing an analogy to double quantum dots, we argue that the spectral width of the elastic resonance is determined by the lifetime broadening $h\it{\Gamma}$ of the emitter and detector states. Good agreement with the model is found also in an experiment in which the charge transfer is in the regime $h\it{\Gamma}\gg k_{\rm{B}}T$. By performing spectroscopy below the Fermi energy, we furthermore observe elastic and inelastic transfer of holes. 
Clemens R\"ossler, Simon Burkhard, Tobias Kr\"ahenmann, Marc   R\"o\"osli, Peter M\"arki, Julien Basset, Thomas Ihn, Klaus E...
cond-mat.mes-hall quant-ph