Critical contacts

Superconducting single-molecule transistors have been realized using single C₆₀ molecules.

Credit: © 2009 NPG

Experimental research on single-molecule transistors based on molecular magnets has yielded a wealth of fundamental information about single-spin dynamics and potential applications in quantum computing. However, despite extensive theoretical studies, superconducting single-molecule transistors have remained elusive. Clemens Winkelmann and colleagues at the Joseph Fourier University have now demonstrated the realization of superconducting single-molecule transistors using single C₆₀ molecules¹.

The researches coupled gated-C₆₀ quantum dots with superconducting contacts of aluminium or aluminium/gold junctions. The superconducting contacts resolved the resistive limitations of normal-state contacts. The device structures were produced by dropping a solution of toluene containing C₆₀ onto thin metallic wires fabricated on top of Al/Al₂O₃ backgates. The nanowires were then broken by applying a voltage between the electrodes at 4 K — a technique known as electromigration — so as to leave a small gap in the wire containing a single C₆₀ molecule.

The conductivity of 11 devices, measured at 40 mK, were found to depend on the gate voltage. Furthermore, the devices showed Coulomb blockade and features associated with the Kondo effect. The structures could potentially be integrated with superconducting quantum interference devices (SQUID) for molecular Q-bit architectures.