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Reducing the dimensionality of bulk materials to atomically thin films allows for exploration of novel phases. The carrier density often plays a crucial role in accessing these phases. Using a persistent all-optical gating effect, local control over the carrier density in graphene, MoS₂, phosphorene, and a thin layer of (Bi,Sb)₂Te₃ on SrTiO₃ substrates has been recently demonstrated [1,2,3]. The effect is postulated to originate from a reversible optically modulated space-charge region in the SrTiO₃, though exact details of the mechanism, such as the role of various defects and its relation to other optically induced persistent phenomena, have remained unclear. Using Kelvin probe microscopy, conductivity measurements, and optical transmission spectroscopy of graphene on SrTiO₃, combined with density-functional calculations, we address outstanding questions on the role of defects, and provide ways to engineer and enhance the effect.

[1] A. L. Yeats et al., Sci. Adv. 1, e1500640 (2015)
[2] E. C. Vincent et al., in prep (2017)
[3] F. Liu et al., Adv. Mat. 28, 7768 (2016)