Content area
Full Text
LETTERS
PUBLISHED ONLINE: 25 MARCH 2012 | http://www.nature.com/doifinder/10.1038/nnano.2012.37
Web End =DOI: 10.1038/NNANO.2012.37
Observation of quantum interference in molecular charge transport
Constant M. Gudon1, Hennie Valkenier2, Troels Markussen3, Kristian S. Thygesen3, Jan C. Hummelen2 and Sense Jan van der Molen1*
As the dimensions of a conductor approach the nanoscale, quantum effects begin to dominate, and it becomes possible to control the conductance through direct manipulation of the electron wavefunction. Such control has been demonstrated in various mesoscopic devices at cryogenic temperatures14, but
it has proved to be difcult to exert control over the wavefunction at higher temperatures. Molecules have typical energy level spacings (eV) that are much larger than the thermal
energy at 300 K (25 meV), and are therefore natural candi
dates for such experiments. Previously, phenomena such as giant magnetoresistance5, Kondo effects6 and conductance switching711 have been observed in single molecules, and theorists have predicted that it should also be possible to observe quantum interference in molecular conductors1218, but until
now all the evidence for such behaviour has been indirect. Here, we report the observation of destructive quantum interference in charge transport through two-terminal molecular junctions at room temperature. We studied ve different rigid p-conjugated molecular wires, all of which form self-assembled monolayers on a gold surface, and nd that the degree of interference can be controlled by simple chemical modications of the molecular wire.
The conductance properties of solid-state mesoscopic structures are dominated by quantum effects at low temperatures. For example, if partial electron waves propagating through the two branches of a ring-shaped mesoscopic structure interfere with each other destructively, conductance is suppressed, and if they interfere constructively, conductance is enhanced1,4. Similar behaviour is expected to occur for certain classes of molecular junctions1319, with the
interference occurring between electron waves propagating through molecular orbitals that are separated in both space and energy. Because the properties of molecular orbitals can be manipulated by chemical design, it should be possible to tune the conductance of single-molecule junctions over orders of magnitude at ambient temperatures. Although variations in charge-transfer rates within donorbridgeacceptor molecules can be explained in terms of interference20,21, until now, all the evidence for quantum inter
ference in molecular conductance experiments has been indirect2224.
Here, we provide direct evidence for destructive quantum interference in...