Tunable and laser-reconfigurable 2D heterocrystals obtained by epitaxial stacking of crystallographically incommensurate Bi₂Se₃ and MoS₂ atomic layers

Vertical stacking is widely viewed as a promising approach for designing advanced functionalities using twodimensional (2D) materials. Combining crystallographically commensurate materials in these 2D stacks has been shown to result in rich new electronic structure, magnetotransport, and optical properties. In this context, vertical stacks of crystallographically incommensurate 2D materials with well-defined crystallographic order are a counterintuitive concept and, hence, fundamentally intriguing. We show that crystallographically dissimilar and incommensurate atomically thin MoS₂ and Bi₂Se₃ layers can form rotationally aligned stacks with longrange crystallographic order. Our first-principles theoretical modeling predicts heterocrystal electronic band structures, which are quite distinct from those of the parent crystals, characterized with an indirect bandgap. Experiments reveal striking optical changes when Bi₂Se₃ is stacked layer by layer on monolayer MoS₂, including 100% photoluminescence (PL) suppression, tunable transmittance edge (1.1→0.75 eV), suppressed Raman, and wide-band evolution of spectral transmittance. Disrupting the interface using a focused laser results in a marked the reversal of PL, Raman, and transmittance, demonstrating for the first time that in situ manipulation of interfaces can enable "reconfigurable" 2D materials. We demonstrate submicrometer resolution, "laserdrawing" and "bit-writing," and novel laser-induced broadband light emission in these heterocrystal sheets.