Photoluminescence Detection of Polytype Polarization in r-MoS2 Enabled by Asymmetric Dielectric Environments.

The rhombohedral (r) polytypes of transition metal dichalcogenides (TMDs) constitute a class of 2D ferroelectric materials, where lateral shifts between parallel layers induce reversible out-of-plane polarization. This emerging field, known as SlideTronics, holds significant potential for next-generation electronic and optoelectronic applications. Previous research has extensively studied how electrical and chemical doping affects excitonic signatures in conventional 2H-TMDs and how dielectric environments influence their optical properties. However, the impact of intrinsic polarization of these ferroelectric materials in asymmetric dielectric environments remains largely unexplored. Here, we demonstrate a striking polarization-dependent photoluminescence (PL) contrast of up to 400% between ferroelectric domains in bilayer and trilayer rhombohedral molybdenum disulfide (r-MoS2). This pronounced contrast arises from an asymmetric dielectric environment, which induces polarization-dependent shifts in the Fermi energy, leading to modulation of the exciton-trion population balance. A detailed temperature-dependent line shape analysis of the PL, conducted from 4 K to room temperature, reveals domain-specific trends that further reinforce the connection between polarization states and excitonic properties. The persistence of these distinct optical signatures at room temperature establishes PL as a robust and noninvasive probe for ferroelectric domain characterization, particularly in fully encapsulated device architectures where conventional techniques, such as Kelvin probe force microscopy, become impractical.