Abstract
The Rashba splitting in hybrid organic–inorganic lead–halide perovskites (HOIP) is particularly promising and yet controversial, due to questions surrounding the presence or absence of inversion symmetry. Here we utilize two-photon absorption spectroscopy to study inversion symmetry breaking in different phases of these materials. This is an all-optical technique to observe and quantify the Rashba effect as it probes the bulk of the materials. In particular, we measure two-photon excitation spectra of the photoluminescence in 2D, 3D, and anionic mixed HOIP crystals, and show that an additional band above, but close to the optical gap is the signature of new two-photon transition channels that originate from the Rashba splitting. The inversion symmetry breaking is believed to arise from ionic impurities that induce local electric fields. The observation of the Rashba splitting in the bulk of HOIP has significant implications for the understanding of their spintronic and optoelectronic device properties.
Highlights
The Rashba splitting in hybrid organic–inorganic lead–halide perovskites (HOIP) is promising and yet controversial, due to questions surrounding the presence or absence of inversion symmetry
The Dresselhaus effect, as described in zinc blende semiconductors[1], originates from bulk crystal structures that lack inversion symmetry, while the Rashba effect, originally described in wurtzite crystals[2], and reformulated in the Bychkov–Rashba model for 2D electron gases[3], results from inversion asymmetry that arises from site point group dipoles of constituent atoms that add up to a non-zero vector that can point in the direction of either a bulk inversion asymmetry (“bulk Rashba materials”) or a structural inversion asymmetry such as in the case of surfaces or heterojunctions in quantum wells[4]
We show that inversion symmetry breaking and Rashba-splitting are correlated with the presence of ionic defects in the crystals and can be attributed to local electric fields
Summary
The Rashba splitting in hybrid organic–inorganic lead–halide perovskites (HOIP) is promising and yet controversial, due to questions surrounding the presence or absence of inversion symmetry. The resulting spectrum will show a double-peaked structure, with maximal TPA occurring when 2_ω determined is by above ERcðvÞ, the the band-gap energy EG Rashba energy splitting by an amount associated with the conduction (valence) bands
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