Experimental Evidence for Coulomb Charging Effects in an Open Quantum Dot at Zero Magnetic Field

We have measured the low-temperature transport properties of an open quantum dot formed in a clean one-dimensional channel. For the first time, at zero magnetic field, continuous and periodic oscillations superimposed upon ballistic conductance steps are observed when the conductance through the dot $G$ exceeds ${2e}^2/h$. We ascribe the observed conductance oscillations to evidence for Coulomb charging effects in an open dot. This is supported by the evolution of the oscillating features for $G>\mathrm{}{2e}^2/h$ as a function of both temperature and barrier transparency.