We use a novel technique to experimentally explore transport properties through a single metallic nanoparticle with variable coupling to electric leads. For strong dot-lead coupling the conductance is an oscillatory function of the gate voltage with perio dicity determined by the charging energy, as expected. For weaker coupling we observe the appearance of additional multi-periodic oscillations of the conductance with the gate voltage. These harmonics correspond to a change of the charge on the dot by a fraction of an electron. This notion is supported by theoretical calculations based on dissipative action theory. Within this framework the multiple periodicity of the conductance oscillations arises due to non-pertubative instanton solutions.
We have studied the transport through metallic quantum dots while controllably varying its coupling to the leads. We find that on the route towards fully opening, the system passes through intermediate coupling regime, in which the conductance shows multi periodic oscillations with the gate voltage. We attribute these oscillations to the charging of the dot by a fraction of an electron. This notion is supported by calculations based on the dissipative action theory.