Encoding multistate charge order and chirality in endotaxial heterostructures

High-density phase change memory (PCM) storage is proposed for materials with multiple intermediate resistance states, which have been observed in 1$T$-TaS$_2$ due to charge density wave (CDW) phase transitions. However, the metastability responsible for this behavior makes the presence of multistate switching unpredictable in TaS$_2$ devices. Here, we demonstrate the fabrication of nanothick verti-lateral $H$-TaS$_2$/1$T$-TaS$_2$ heterostructures in which the number of endotaxial metallic $H$-TaS$_2$ monolayers dictates the number of resistance transitions in 1$T$-TaS$_2$ lamellae near room temperature. Further, we also observe optically active heterochirality in the CDW superlattice structure, which is modulated in concert with the resistivity steps, and we show how strain engineering can be used to nucleate these polytype conversions. This work positions the principle of endotaxial heterostructures as a promising conceptual framework for reliable, non-volatile, and multi-level switching of structure, chirality, and resistance.