Electronic transport in one-dimensional mesoscopic systems
Mercredi 26/03/2008, 11:00
SPEC Salle Itzykson, Bât.774, Orme des Merisiers
One-dimensional electron systems are have been predicted to be
fundamentally different from those in higher dimensions, particularly with
respect to the way in which interactions are screened. While theoretical
work on these systems dates back to the 1950s, it has only been since 1990
that the fabrication and investigation of truly one-dimensional systems on
the nanometer scale have been made possible by advances in chemistry and
molecular beam epitaxy.
During my Ph.D. in the group of David Goldhaber-Gordon, I performed transport
measurements on three systems - carbon nanotubes, carbon nanotube peapods
and 'cleaved edge overgrowth' GaAs hole wires - each of which enables the
investigation of a different aspect of one-dimensional physics.
For this presentation I shall give a brief introduction to one- and
zero-dimensional physics and then --- due to time constraints --- discuss
primarily the peapod measurements in three parts:
(1) We found, rather unexpectedly, that the periodically intercalated C60
molecules do not significantly modify the nanotube's electonic structure
near the Fermi level.
(2) We were able to carefully study in these devices the evolution of the
spin-1/2 Kondo effect in a magnetic field, on which there has been some
theoretical controversy. We find that existing theories agree with the
experimental data qualitatively but not in their details.
(3) We observed an underscreened spin-1 Kondo effect. Performing the first
tuning of the transition between singlet and triplet ground states
independently with a gate voltage and magnetic field, we find that for the
most part our data are explained by a simple model; however, some puzzles
I shall also briefly touch upon the measurements of carbon nanotubes and
CEO quantum wires. (Further details for these may be provided in a future
Quantronics Group seminar.)