Absence of large valence band Rashba splitting in metal halide perovskites

Organic and inorganic lead halide perovskites share the same properties of high efficiency in energy conversion and high spin-orbit interaction. For both, a large Rashba effect has been invoked to be responsible for the high efficiency by prohibiting direct recombination. In the valence band of methylammonium lead bromide a static Rashba effect has been reported by angle-resolved photoemission (ARPES) and circular dichroism with giant values of 0.7 to 1.1 eV nm [1]. We present precise ARPES band dispersion measurements of methylammonium lead bromide and cesium lead bromide to show that a Rashba effect of the reported size does not exist. Moreover, we use spin-resolved ARPES to confirm the conclusions. We also observe a large circular dichroism effect and demonstrate that this effect does not imply any measurable spin polarization and Rashba effect. Our results exclude a static Rashba effect in the valence band as origin of the high efficiency of metal halide perovskites.
[1] D. Niesner et al., Phys. Rev. Lett. 117, 126401 (2016).