The Kondo Effect in C₆₀ Single-Molecule Transistors

Abstract

We have used an electromigration technique to fabricate C 60 -based single-molecule transistors. We detail the process statistics and the protocols used to infer the successful formation of a single-molecule transistor. At low temperatures each transistor acts as a single-electron device in the Coulomb blockade regime. Resonances in the differential conductance indicate vibrational excitations consistent with a known mode of C 60 . In several devices we observe conductance features characteristic of the Kondo effect, a coherent many-body state comprising an unpaired spin on the molecule coupled by exchange to the conduction electrons of the leads. The inferred Kondo temperature typically exceeds 50 K, and signatures of the vibrational modes persist into the Kondo regime.

Molecular three-terminal devices: fabrication and measurements

“…[8][9][10][11][12] To be more specific, a surprising feature of the data in Fig. 7 is the absence of degeneracy points along the gate axis for low bias.…”

“…It is important to note that at low temperatures up to now three-terminal measurements on molecular junctions have all shown Coulomb blockade features [8][9][10][11][12] including the Kondo effect. 9,10,12 Our measurements presented in the previous section, however, show that Coulomb blockade itself is not a distinctive feature. In the remainder of this paper, we present two measurements with different molecules that may provide information about the presence of molecules in the gap.…”

“…With the gate, the molecule can be oxidized or reduced and tuned between nonconducting and conducting states. [8][9][10][11][12] The extent to which the orbital levels can be shifted up and down is controlled by the gate coupling parameter. This parameter is related to the gain of the device and in Coulomb theory it equals the ratio of the gate capacitance to the total capacitance of the islands.…”

Mechanically Adjustable and Electrically Gated Single-Molecule Transistors

“…Therefore we first break the wires partially or fully at 4.2 K using electromigration, a technique used previously to make nm-scale gaps for molecular transistors [20,[4][5][6][7].…”

“…We chose C 60 molecules because they have been used successfully to make single-5 molecule transistors [4,7]. To fabricate C 60 devices, we first clean unbroken Au wires in acetone, isopropanol, and oxygen plasma.…”