Giant Rashba-splitting in 2D organic-inorganic halide perovskites measured by optical modulation spectroscopies*

Two-dimensional (2D) layered hybrid organic-inorganic halide perovskite semiconductors form natural ‘multiple quantum wells’ that possess strong spin-orbit coupling due to the heavy elements in their building blocks. This may lead to ‘Rashba-splitting’ (RS) close to the extrema in the electron bands. We have employed a plethora of ultrafast transient, electro-absorption magneto-optical spectroscopies, and theoretical calculations for studying the primary (excitons) and long-lived (free-carriers) photoexcitations in thin films of 2D perovskite, namely (C₆H₅C₂H₄NH₃)₂PbI₄ [1]. The density functional theory calculation shows the occurrence of RS in the plane perpendicular to the growth direction. From the electroabsorption spectrum [2] and photoinduced absorption spectra from excitons and free-carriers we indeed obtain a giant RS in this compound, with energy splitting of ~40 meV and Rashba parameter of ~1.6 eV Angstrom; which are among the highest RS size parameters reported so far. The influence of the RS on the magneto-optical properties of this compound has been measured by field induced circular dichroism and polarization at high magnetic field up to 25T. We found that the exciton absorption and photoluminescence emission spectra split due to the RS, and show g-values that are considerable shifted from that of the free electron.
[1] Y. Zhai, S. Baniya, C. Zhang, C.-X. Sheng, E. Ehrenfreund, Z.V. Vardeny, Science Advances 3, e1700704 (2017).
[2] E. Amerling, S. Baniya, E. Lafalce, C. Zhang, Z. V. Vardeny, and L. Whittaker-Brooks, Jour. Phys. Chem. Lett. 8, 4557 (2017).