Novel Quantum Transport Phenomena in Molecular Junctions

• Applicant: Professor Dr. Felix von Oppen
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2006 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 25125737

By virtue of their enormous variability, single-molecule devices offer a fascinating arena for realizing novel effects in quantum transport through nanostructures. A natural source for such effects lies in the coupling of the electronic degrees of freedom to few, well-defined molecular vibrations. This coupling is specific to molecules as opposed to conventional nanostructures such as quantum dots, where one commonly deals with a continuum of phonon modes. One expects new regimes of quantum transport for at least two reasons: (i) The transport current can excite nonequilibrium molecular vibrations. We predicted that this can lead to current flow in the form of a self-similar hierarchy of avalanches of many electrons. (ii) Polaron shifts of the molecular levels can renormalize the charging energy to negative values, analogous to negative-U centers in amorphous semiconductors. Very recently, we showed that transport through such negative-U molecules is dominated by tunneling of electron pairs.We propose to study these interesting modes of transport through molecular junctions by pursuing a two-pronged research program. First, we will push to understand transport in these situations beyond the rate-equation regime, which is expected to uncover additional physics. Second, we will go beyond the minimal model of molecular junctions employed in previous studies in an effort to achieve a more realistic and complete description of possible experimental systems. Finally, we will also search for further novel modes of quantum transport in molecular junctions.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1243: Quantum Transport at the Molecular Scale