Direct evidence of a charge depletion region at the interface of van der Waals monolayers and dielectric oxides: The case of superconducting FeSe/STO

Abstract

Monolayers of two-dimensional (2D) van der Waals (vdW) materials grown on dielectric oxides exhibit unprecedented physical properties. For example, the superconducting transition temperature of an FeSe monolayer on ${\mathrm{SrTiO}}_{3}$ is by far higher than its bulk counterpart. However, how the charge distribution across the interface looks like and how it helps to improve these properties is hitherto unknown. Here, using momentum- and energy-resolved high-resolution electron spectroscopy, we probe the dynamic charge response of the $\mathrm{FeSe}/{\mathrm{SrTiO}}_{3}(001)$ heterostructures and, thereby, demonstrate the existence of a charge depletion layer at the interface. The presence of this depletion layer, accompanied with a considerably large charge transfer, leads to a renormalization of the ${\mathrm{SrTiO}}_{3}$ energy bands and a substantial band bending at the interface. Our discovery paves the way for designing novel 2D superconductors through interface engineering. The phenomenon is expected to occur at the interface of many vdW monolayers and dielectric oxides.