  We report temperature-dependent spectroscopy on the layered (n=4)
two-dimensional (2D) Ruddlesden-Popper perovskite (BA)(MA)PbI.
Helicity-resolved steady-state photoluminescence (PL) reveals no optical degree
of polarization. Time-resolved PL shows a photocarrier lifetime on the order of
nanoseconds. From simultaneaously recorded time-resolved differential
reflectivity (TR$\Delta$R) and time-resolved Kerr ellipticity (TRKE), a
photocarrier lifetime of a few nanoseconds and a spin dephasing time on the
order of picoseconds was found. This stark contrast in lifetimes clearly
explains the lack of spin polarization in steady-state PL. While we observe
clear temperature-dependent effects on the PL dynamics that can be related to
structural dynamics, the spin dephasing is nearly T-independent. Our results
highlight that spin dephasing in 2D (BA)(MA)PbI occurs at time scales faster
than the exciton recombination time, which poses a bottleneck for applications
aimingto utilize this degree of freedom.
