Reorganization of CDW stacking in 1T-TaS₂ by light and an in-plane electrical bias

Light-matter interaction in strongly correlated materials is interesting because light can significantly alter the free energy landscape of strong correlations resulting in many new physical phenomena. Though light-induced changes in the lattice, electrical, and magnetic properties have been extensively studied before, linear optical constants and their sensitivity to stimuli remain much to be explored. Recently, we studied the optical properties of 1T-TaS₂ under electrical bias and different illumination conditions. We observed fast tunable optical properties of this material arising from the reorganization of charge density wave (CDW) stacking. Our experimental investigation suggested that CDW domains in 1T-TaS₂ can absorb low-intensity incoherent white light to switch their stacking configuration in a sub-microsecond timescale. The change in stacking configuration results in a unity-order change in refractive index at room temperature at illumination intensities of just 1-Sun. This stacking reorganization showed temperature dependence and persisted at lower temperatures. Further, the stacking reorganization under illumination favored a high-energy stacking configuration. Our investigation has provided an insight into the mechanism of tuning and demonstrated that light is a powerful probe to map and control the energy landscape of strong correlations in quantum materials.