Experimental evidence of Kondo effect induced by oxygen-vacancy in IrO2 crystals

Abstract

The study of well-known electrocatalyst iridium dioxide (IrO2) has been renewed recently because of its interesting topological properties and orbital two channels Kondo effects. To solidly build up the orbital Kondo effect in IrO2, we here grew the IrO2 single crystal that is most suitable to elucidate its intrinsic physical properties, and then studied its Kondo effect through electrical transport, magnetic characterizations, Raman spectroscopy. Electrical transport and magnetoresistance of IrO2 show a low-temperature upturn in resistivity together (<25 K) with isotropic magnetoresistance, which are consistent with Kondo-like transport behaviors. Combined with the analysis of magnetic and X-ray photoelectron spectroscopy data verifies that the point defects in IrO2 are paramagnetic impurity-oxygen vacancies. These results suggest that IrO2 does have the Kondo effect resulted from the oxygen vacancies, rather than the conventional Kondo effect induced by magnetic impurities.