Superatoms and Molecular Machines

Using low temperature scanning tunneling microscopy (LT-STM) and density functional theory, we explore the inner secrets of hollow molecules, such as fullerenes and nanotubes.  By imaging the local density of states of C₆₀ molecules at various bias voltages we have discovered electronic states whose images are reminiscent of spherical harmonic probability densities of atoms.  For these "superatom states" the electronic wave functions are bound to the hollow molecular core rather then to the individual atomic centers.  The superatom states have a universal origin in the image potential states of molecular sheets, e.g., graphene, and thus should be found in all hollow materials.  The superatom states are intriguing because of their nonnuclear density maxima, which could provide a new paradigm for charge transport in molecular electronics.

In other experiments we explore the electronic structure and dynamics of molecular machines.  Of particular interest are endohedral fullerenes, which contain an atom or molecule within the carbon cage.  We are exploring the endohedral particle dynamics under the stimulation by tunneling electrons and light.  These experiemntal and theoretical collaborations involve Prof. Lothar Dunsch of Leibniz Intitute, Dresden, and Prof. Tamar Seideman of Northwestern University.