Unity-order refractive index tunability at room temperature in 1T-TaS₂, a strongly correlated material

Strongly correlated materials could greatly respond to a stimulus due to their collective behavior. Thus, strongly correlated materials are well studied in the past for their tunable properties, especially electrical and thermal. However, their optical properties remain to be explored. In this work, we study the optical properties of 1T-TaS₂, a quasi-2D material supporting charge density waves (CDW). 1T-TaS₂ is the only material to exhibit a nearly commensurate CDW phase at room temperature and its electrical and thermal properties are shown to exhibit a large change with temperature, DC and AC biases, pressure, and light. Here, we study the optical properties of 1T-TaS₂ under DC and AC biases, different intensities of optical illumination, and at different temperatures. Under all these conditions, we observe a unity-order change in the refractive index of thin films of 1T-TaS₂. We hypothesize that the stacking of CDWs in this material changes with stimulus resulting in its optical constants to change. ARPES and STM measurements are underway to verify the hypothesis. Our discovery of the large tunability of optical constants of 1T-TaS₂ presents opportunities in studying light-matter interaction in strongly correlated materials and its application to nanophotonic devices.