Very high Kondo temperature ($T_{K}\sim $ 80 K) in single self-assembled InAs quantum dots coupled to metallic nanogap electrodes

We have studied electron tunneling through single self-assembled InAs quantum dots (QDs) laterally coupled to metallic nanogap electrodes. Lateral electron tunneling structures were fabricated by forming nanogap metallic electrodes directly upon single self-assembled InAs QDs grown on GaAs surfaces. The n-type substrate was used as a backgate electrode. Although no intentional tunneling barriers were introduced, the fabricated samples worked as single electron transistors and exhibited Coulomb blockade effect. Furthermore, a clear spin-half Kondo effect was observed when strong coupling between the electrodes and the QDs was realized using a large QD with a diameter of $\sim $100 nm. From the temperature dependence of the linear conductance at the Kondo valley, the Kondo temperature, $T_{K}$, was determined to be $\sim $ 81 K. This is the highest $T_{K}$ ever reported for artificial semiconductor nanostructures. This high Kondo temperature is due to strong QD-electrode coupling and large charging/orbital-quantization energies in our self-assembled InAs QD structures.