Evolution of the Coulomb gap in tunnel-coupled quantum dots

We report differential conductance measurements through a double quantum dot with adjustable interdot tunneling rate. The Coulomb gap of the double dot decreases continuously as the interdot tunnel conductance $G_{\mathrm{int}}$ is increased, from the gap of two isolated dots (when $G_{\mathrm{int}}\text{∼0)}$ to the gap of a single large dot of twice the total capacitance (when $G_{\mathrm{int}}{\text{=2e}}^2\mathrm{/h).}$ Excited electronic states in differential conductance measurements on single dots show a spectrum which is essentially independent of the number of electrons in the dot, but is not uniform.