Resistively detected nuclear magnetic resonance in n- and p-type GaAs quantum point contacts.

We present resistively detected NMR measurements in induced and modulation-doped electron quantum point contacts, as well as induced hole quantum point contacts. While the magnitude of the resistance change and associated NMR peaks in n-type devices is in line with other recent measurements using this technique, the effect in p-type devices is too small to measure. This suggests that the hyperfine coupling between holes and nuclei in this type of device is much smaller than the electron hyperfine coupling, which could have implications in quantum information processing.

Electronic and optical properties of electromigrated molecular junctions.

Electromigrated nanoscale junctions have proven very useful for studying electronic transport at the single-molecule scale. However, confirming that conduction is through precisely the molecule of interest and not some contaminant or metal nanoparticle has remained a persistent challenge, typically requiring a statistical analysis of many devices. We review how transport mechanisms in both electronic and optical measurements can be used to infer information about the nanoscale junction configuration.

Three-terminal devices to examine single-molecule conductance switching.

We report electronic transport measurements of single-molecule transistor devices incorporating bipyridyl-dinitro oligophenylene-ethynylene dithiol (BPDN-DT), a molecule known to exhibit conductance switching in other measurement configurations. We observe hysteretic conductance switching in 8% of devices with measurable currents and find that dependence of the switching properties on gate voltage is rare when compared to other single-molecule transistor devices. This suggests that polaron formation is unlikely to be responsible for switching in these devices.

Neutral complexes of first row transition metals bearing unbound thiocyanates and their assembly on metallic surfaces.

A series of transition metal coordination complexes designed to assemble on gold surfaces was synthesized, their electronic structure and transitions analyzed, and their magnetic properties studied. By taking advantage of recently developed thiocyanate assembly protocols, these molecules were then assembled onto a gold surface, without the need for an inert atmosphere, to give a loosely packed monolayer. The assembled molecules exhibit properties similar to that of the bulk molecules, indicating little change in molecular structure outside of chemisorption.

Kondo resonances and anomalous gate dependence in the electrical conductivity of single-molecule transistors.

We report Kondo resonances in the conduction of single-molecule transistors based on transition metal coordination complexes. We find Kondo temperatures in excess of 50 K, comparable to those in purely metallic systems. The observed gate dependence of the Kondo temperature is inconsistent with observations in semiconductor quantum dots and a simple single-dot-level model.