Transport spectroscopy of a confined electron system under a gate tip

Conductance resonances measured for split-gate structures around threshold are interpreted in terms of single-electron tunneling through a quantum dot beneath the tip of the gate finger. Measurements at different values of source-drain voltage allow the spectroscopy of excited states for a fixed number of electrons in the quantum dot. The measured magnetic-field dependence of the conductance resonances is consistent with a minimal number of seven electrons in the quantum dot.