Resonant tunneling through zero-dimensional impurity states: Effects of   a finite temperature
  We have performed temperature dependent tunneling experiments through a single impurity in an asymmetric vertical double barrier tunneling structure. In particular in the charging direction we observe at zero magnetic field a clear shift in the onset voltage of the resonant tunneling current through the impurity. With a magnetic field applied the shift starts to disappear. The experimental observations are explained in terms of resonant tunneling through a spin degenerate impurity level. 
P. K\"onig, U. Zeitler, J. K\"onemann, T. Schmidt, R.J. Haug