Insulator-metal transition induced by interlayer coupling in La0.6Sr0.4MnO3/SrTiO3 superlattices

Abstract

The electronic and magnetic properties of perovskite superlattices composed of five unit-cell layers of ferromagnetic metal ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_3$ and nonmagnetic band insulator ${\mathrm{SrTiO}}_3$ with varying layer thickness have been systematically investigated. The superlattices have well-defined periodic stacking with no sign of interlayer diffusion. The spin canting at the interfaces in ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_3$ layers manifests itself as a suppressed magnetization and huge magnetoresistance subsisting to low temperature. The transport properties show a clear crossover from insulating to metallic perhaps by an increase in the interlayer electron hopping through ${\mathrm{SrTiO}}_3$ layers when the ${\mathrm{SrTiO}}_3$ layer thickness is reduced. This crossover is also discerned in the infrared optical spectra as the filling of absorption in the low-energy region.