Spectroscopy of the Single-Particle States of a Quantum-Dot Molecule

We investigate low-temperature transport through two identical vertically coupled quantum dots in a triple-barrier heterostructure. The current-voltage curve exhibits two series of current steps of different magnitude. On the basis of magnetotunneling measurements, we relate the current steps to the single-particle levels of a quantum-dot molecule. From the absence of many-particle phenomena, an upper limit of 1 ns is determined for the energy-relaxation time in the double-dot system.