Gate tuning and universality of Two-stage Kondo effect in single molecule transistors

Using single molecule transistor incorporating individual Manganese phthalocynine (MnPc) molecules, we studied two-stage Kondo effect involving a multi-level impurity. Utilizing extreme confined molecular structure, we have achieved gate tuning of Kondo temperatures for single channel two-stage Kondo process. Single gate in our devices can significantly change the Kondo temperature T* representing the internal correlation between different molecular levels. A linear relationship was obtained between the T* and effective interaction of two electrons, and exchange energy of electrons in this molecule device could be extracted accordingly. Moreover, the two-stage Kondo resonance behaves almost identical to small excitations in electric field, magnetic field and thermal change, showing a clear universality. Messages learned in this study not only fill in missing experimental knowledge of evolution in two-stage Kondo resonance toward the quantum phase transition point, but also help in understanding sophisticated molecular electronic spectroscopy in strong correlation regime.