Nonlocality of the exchange interaction probed by scanning tunneling spectroscopy - art. no. 201301

The energy states of the tip induced quantum dot are investigated in a magn etic field as a function of the tip position with respect to the surface. T o study the influence of potential perturbations on the exchange interactio n in the quantum dot, emphasis is given on the Landau and spin levels probe d at positive bias. Mapping of the spatial dependence of the peak energies and comparison with the surface potential map-reconstructed from the analys is of scattering states around ionized dopants-reveals that the fluctuating surface potential acts as a local perturbation on the quantum dot states. In contrast, the spin splitting is influenced nonlocally by the surface pot ential, which directly evidences the nonlocal character of the exchange int eraction.