Quantum chaos with non-periodic, complex orbits in the Resonant   Tunneling Diode
  We show that a special type of orbits, which are non-periodic and complex, 'Saddle Orbits' (SOs) describe accurately the quantal and experimental current oscillations in the Resonant Tunneling Diode in tilted fields. This is the first demonstration that one needs to abandon the periodic orbits (POs) paradigm in favour of this new and peculiar type of orbit. The SOs solve the puzzle of broad regions of experimental oscillations where we find no real or complex PO that can explain the data. The SOs succeeds in regimes involving several non-isolated POs, where PO formulas fail. 
D.S. Saraga and T.S. Monteiro