RT Journal Article SR Electronic T1 Excitons in 2D perovskites for ultrafast terahertz photonic devices JF Science Advances JO Sci Adv FD American Association for the Advancement of Science SP eaax8821 DO 10.1126/sciadv.aax8821 VO 6 IS 8 A1 Kumar, Abhishek A1 Solanki, Ankur A1 Manjappa, Manukumara A1 Ramesh, Sankaran A1 Srivastava, Yogesh Kumar A1 Agarwal, Piyush A1 Sum, Tze Chien A1 Singh, Ranjan YR 2020 UL http://advances.sciencemag.org/content/6/8/eaax8821.abstract AB In recent years, two-dimensional (2D) Ruddlesden-Popper perovskites have emerged as promising candidates for environmentally stable solar cells, highly efficient light-emitting diodes, and resistive memory devices. The remarkable existence of self-assembled quantum well (QW) structures in solution-processed 2D perovskites offers a diverse range of optoelectronic properties, which remain largely unexplored. Here, we experimentally observe ultrafast relaxation of free carriers in 20 ps due to the quantum confinement of free carriers in a self-assembled QW structures that form excitons. Furthermore, hybridizing the 2D perovskites with metamaterials on a rigid and a flexible substrate enables modulation of terahertz fields at 50-GHz modulating speed, which is the fastest for a solution-processed semiconductor-based photonic device. Hence, an exciton-based ultrafast response of 2D perovskites opens up large avenues for a wide range of scalable dynamic photonic devices with potential applications in flexible photonics, ultrafast wavefront control, and short-range wireless terahertz communications.