Inelastic cotunneling through an excited state of a quantum dot
Abstract
We consider the transport spectroscopy of a quantum dot with an even number of electrons at finite bias voltage within the Coulomb blockade diamond. We calculate the tunneling current due to the elastic and inelastic cotunneling processes associated with the spinsinglet ground state and the spintriplet first excited state. We find a step in the differential conductance at a bias voltage equal to the excitation energy with a peak at the step edge. This may explain the recently observed sharp features in finite bias spectroscopy of semiconductor quantum dots and carbon nanotubes. Two limiting cases are considered: (i) for a low excitation energy, the excited state can decay only by inelastic cotunneling due to Coulomb blockade (ii) for a higher excitation energy the excited state can decay by sequential tunneling. We consider two spindegenerate orbitals that are active in the transport. The nonequilibrium state of the dot is described using master equations taking spin degrees of freedom into account. The transition rates are calculated up to second order in perturbation theory. To calculate the current we derive a closed set of master equations for the spinaveraged occupations of the transport states.
 Publication:

arXiv eprints
 Pub Date:
 March 2001
 arXiv:
 arXiv:condmat/0103579
 Bibcode:
 2001cond.mat..3579W
 Keywords:

 Condensed Matter  Mesoscopic Systems and Quantum Hall Effect;
 Condensed Matter  Disordered Systems and Neural Networks