Negative differential resistance due to single-electron switching
  We present the multilevel fabrication and measurement of a Coulomb-blockade device displaying tunable negative differential resistance (NDR). Applications for devices displaying NDR include amplification, logic, and memory circuits. Our device consists of two Al/Al$_{x}$O$_{y}$ islands that are strongly coupled by an overlap capacitor. Our measurements agree excellently with a model based on the orthodox theory of single-electron transport. 
C. P. Heij, D. C. Dixon, P. Hadley, J. E. Mooij (Delft University of   Technology)