Heavy-fermion metallic state and Mott transition induced by Li-ion intercalation in LiV2 O4 epitaxial films

The spinel-type LiV2O4 exhibits heavy-fermion metallic behaviors at low temperatures, but the effect of composition modulation on them is unknown. We realized the epitaxial growth of highly crystalline LiV2O4 films and conducted the electrochemical Li-ion intercalation (electron doping) to investigate systematic variation of transport properties in Li1+xV2O4. We found that adjustment of Li content during pulsed-laser deposition was important to obtain films exhibiting the heavy-fermion metallic behavior comparable to that of a bulk single crystal. At low doping regime (x≤0.5), resistivity increased with increasing electron filling. The slope of their linear T2 dependence also increased in accordance of a Fermi-liquid model. At high doping regime (x>0.5), a Mott transition was observed over a range of Li content where a new spinel phase and the original one coexisted. The results revealed that the electron doping induced enhancement of the electron correlation and the resultant Mott transition.