About carrier's self-trapping and dynamical Rashba splitting in the two-dimensional hybrid perovskite (BA)$_2$(MA)$_2$Pb$_3$I$_{10}$

Abstract

Time- and Angle-Resolved Photoelectron Spectroscopy (tr-ARPES) is employed to monitor photoexcited electrons in the two-dimensional hybrid perovskite (BA)$_2$(MA)$_2$Pb$_3$I$_{10}$. Photoelectron intensity maps are in good agreement with ab-initio calculations of the band structure. The effective mass is $-0.18 \pm 0.02 m_e$ and $0.12 \pm 0.02 m_e$ for holes and electrons, respectively. In the photoexcited state, spin-orbit splitting of the conduction band cannot be resolved. This sets the upper bound of photoinduced Rashba coupling to $α_C<2.5$ eVÅ. The correlated electron-hole plasma evolves in Wannier excitons with Bohr radius of 2.8 nm, while no sign of self-trapping in small polarons is found within the investigated time window of up to 120 ps following photoexcitation.

Figures (4)

• Figure 1: a) Schematic structure of the 2D perovskite (BA)$_2$(MA)$_{n-1}$Pb$_n$I$_{3n+1}$ with $n=3$. b) Brillouin zone of the orthorhombic unit cell. c) Dispersion of electronic states along the $\Gamma-X$ and $\Gamma-S$ and $\Gamma-Z$symmetry directions, obtained with PBE-DFT and including spin-orbit coupling.
• Figure 2: a) Valence band dispersion acquired along the $\Gamma-X-\Gamma'$ direction. Energies have been referred with respect to the valence band maximum. The white dashed line is the valence band dispersion predicted by the ab-initio calculations of Fig. 1c. b) Momentum Distribution Curve (MDC) extracted by integrating in an energy interval of 50 meV around the Valence Band Maximum (VBM). c) EDC extracted by integrating in a wavevector interval of 0.05 Å$^{-1}$ around $\Gamma'$.
• Figure 3: a-f) Time resolved ARPES map along $\Gamma-X$ for different pump probe delays. With respect to the valence band map, the energy scale has been shifted by the optical gap $\Delta$. The white line is the conduction band dispersion predicted by ab-initio calculations of Fig. 1c.
• Figure 4: Momentum Distribution Curves extracted at the CBM for delay times of $0.4$ ps (dark circles) and 120 ps (red triangles). The MDCs have been renormalized to the maximum value and fit (solid line) with the model function $|\phi(k)|^2$ described in the text b) Best fitting function of the MDC (black curve) and model MDC curve assuming $\alpha_C=2.5$ eVÅ (shadow pink area).