Current-voltage curves of gold quantum point contacts revisited

We present measurements of current-voltage (I-V) curves on gold quantum poi nt contacts (QPCs) with a conductance up to 4 G(0) (G(0) = 2e(2)/h is the c onductance quantum) and voltages up to 2 V. The QPCs are formed between the gold tip of a scanning tunneling microscope and a Au(110) surface under cl ean ultra-high-vacuum conditions at room temperature. The I - V curves are found to he almost linear in contrast to previous reports. Tight-binding ca lculations of I - V curves for one- and two-atom contacts are in excellent agreement with our measurements. On the other hand, clearly nonlinear I - V curves are only observed when the sample has been cleaned in air. (C) 2000 American Institute of Physics. [S0003-6951(00)02530-4].