Conventional versus singlet-triplet Kondo effect in Blatter radical molecular junctions: Zero-bias anomalies and magnetoresistance

The Blatter radical has been suggested as a building block in future molecular spintronic devices because of its radical character and expected long spin lifetime. However, whether its radical character is maintained in single-molecule junctions depends on the environment. Here, we demonstrate the ability to retain the open-shell nature of the Blatter radical in a two-terminal device by the appearance of a Kondo resonance in transport spectroscopy. Additionally, a high negative magnetoresistance is observed in junctions that do not reveal a zero-bias anomaly. By combining distance-dependent and magnetic-field-dependent measurements and accompanying quantum-chemical and quantum-transport calculations, we show that both findings, the negative magnetoresistance and the Kondo features, can be consistently explained by a singlet-triplet Kondo model. Our findings provide the possibility of using the Blatter radical in a two-terminal system under cryogenic conditions and also reveal the magnetotransport properties emerging from different configurations of the molecule inside a junction.