Quantum Dot Spectroscopy

Research Interests

We have developed cryogenic electrostatic force microscopy (EFM) to determine the shell structure of self-assembled quantum dots. Back-action of a quantum mechanical system on a macroscopic AFM cantilever is at the heart of this unique method that allows energy level spectroscopy of quantum systems without the need of attaching contact leads. We operate at temperatures T which are low enough so that the Coulomb blockade energy of the system is large compared to kT. This allows us to charge the dot electron-by-electron and detect the resultant change in force by EFM techniques. A dc-bias voltage between oscillating tip and sample leads to an effective ac-voltage between a quantum dot and the backelectrode. This ac-voltage modulates the alignment of energy levels between the dot and backelectrode, causing the electron to tunnel into and out of the dot. The motion of the cantilever is damped by the electron tunnelling back and forth, allowing us to perform quantitative energy level spectroscopy.