Differential conductance in atomic-scale metallic contacts

We present exact free-electron calculations of the differential conductance of narrow necks connecting two three-dimensional electron gases. As the voltage increases, the initial quantized values of the conductance evolve into higher or lower noninteger multiples of 2e(2)/h. The contribution of electron tunneling through a region around the constriction is analyzed in terms of a simple model. We show that tunneling can change significatively the shape of the conductance-voltage characteristics. (C) 1998 Elsevier Science B.V. All rights reserved.