Optical probe of electrostatic-doping in ann-type Mott insulator

Abstract

Electrostatic-doping into an $n$-type Mott insulator ${\mathrm{Sm}}_2\mathrm{Cu}{\mathrm{O}}_4$ has been successfully achieved with use of the heterojunction with an $n$-type band semiconductor Nb-doped $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$. The junction exhibits rectifying current-voltage characteristics due to the interface band discontinuity and the formation of depleted region. The application of reverse bias electric field on this junction enables the field-effect electron doping (presumably up to 6% per Cu atom) to the Mott insulator. The electromodulation absorption spectroscopy could clearly show a large modification of the Mott-gap state accompanying the spectral weight transfer to the lower-energy region, reminiscent of formation of a metallic state.