Heavy-fermion metallic state and Mott transition induced by Li-ion intercalation in LiV2O4 epitaxial films

Abstract

The spinel-type ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$ 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 ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$ films and conducted the electrochemical Li-ion intercalation (electron doping) to investigate systematic variation of transport properties in ${\mathrm{Li}}_{1+x}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$. 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 $(x\ensuremath{\le}0.5)$, resistivity increased with increasing electron filling. The slope of their linear ${T}^{2}$ 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.