Optical Study of the Free-Carrier Response of LaTiO3/SrTiO3 Superlattices

We used infrared spectroscopic ellipsometry to investigate the electronic properties of LaTiO₃/SrTiO₃ superlattices (SLs). Our results indicated that, independent of the SL periodicity and individual layer thickness, the SLs exhibited a Drude metallic response with sheet carrier density per interface ≈3×10¹⁴cm^-2. This is probably due to the leakage of d electrons at interfaces from the Mott insulator LaTiO₃ to the band insulator SrTiO₃. We observed a carrier relaxation time ≈35fs and mobility ≈35cm²V^-1s^-1 at 10 K, and an unusual temperature dependence of carrier density that was attributed to the dielectric screening of quantum paraelectric SrTiO₃.