LAUSR

Characterizing and manipulating the circular polarization of light is central to numerous emerging technologies, including spintronics and quantum computing. Separately, monolayer tungsten disulfide (WS2) is a versatile material that has demonstrated promise in a variety of applications, including single photon emitters and valleytronics. Here, we demonstrate a method to tune the photoluminescence (PL) intensity (factor of ×161), peak position (38.4 meV range), circular polarization (39.4% range), and valley polarization of a Bi2Se3-WS2 2D heterostructure using a low-power laser (0.762 μW) in ambient conditions. Changes are spatially confined to the laser spot, enabling submicrometer (814 nm) features, and are long-term stable (>334 days). PL and valley polarization changes can be controllably reversed through laser exposure in a vacuum, allowing the material to be erased and reused. Atmospheric experiments and first-principles calculations indicate oxygen diffusion modulates the exciton radiative vs nonradiative recombination pathways, where oxygen absorption leads to brightening and desorption to darkening.