Mechanically Stable Kondo Resonance in an Organic Radical Molecular Junction

Organic radicals are promising candidates for molecular spintronics due to their intrinsic magnetic moment, their low spin-orbit coupling, and their weak hyperfine interactions. Using a mechanically controlled break junction setup at both room and low temperatures (6 K), we analyze the difference in charge transport between two nitronyl nitroxide radicals (NNR): one with a backbone in the para configuration, the other with a backbone in the meta configuration. We find that para-NNR displays a Kondo resonance at 6 K, while meta-NNR does not. Additionally, the observed Kondo peak in the differential conductance has a roughly constant width independent of the conductance, consistent with a scenario where the molecule is coupled asymmetrically to the electrodes.