  Two-dimensional hybrid organic-inorganic metal halide perovskites offer
enhanced stability for perovskite-based applications. Their crystal structure's
soft and ionic nature gives rise to strong interactions between charge carriers
and ionic rearrangements. Here, we investigate the interaction of
photo-generated electrons and ionic polarizations in single-crystal 2D
perovskite butylammonium lead iodide, varying the inorganic lammelae thickness
in the 2D single crystals. We determined the directionality of the transition
dipole moments of the relevant phonon modes (in the 0.3-3 THz range) by
angle-and-polarization dependent THz transmission measurements. We find a clear
anisotropy of the in-plane photoconductivity, with a 10% reduction along the
axis parallel with the transition dipole moment of the most strongly coupled
phonon. Detailed calculations, based on Feynman polaron theory, indicate that
the anisotropy originates from directional electron-phonon interactions.
