Structural descriptor for enhanced spin-splitting in 2D hybrid perovskites

Abstract

Two-dimensional (2D) hybrid metal halide perovskites have emerged as outstanding optoelectronic materials and are potential hosts of Rashba/Dresselhaus spin-splitting for spin-selective transport and spin-orbitronics. However, a quantitative microscopic understanding of what controls the spin-splitting magnitude is generally lacking. Through crystallographic and first-principles studies on a broad array of chiral and achiral 2D perovskites, we demonstrate that a specific bond angle disparity connected with asymmetric tilting distortions of the metal halide octahedra breaks local inversion symmetry and strongly correlates with computed spin-splitting. This distortion metric can serve as a crystallographic descriptor for rapid discovery of potential candidate materials with strong spin-splitting. Our work establishes that, rather than the global space group, local inorganic layer distortions induced via appropriate organic cations provide a key design objective to achieve strong spin-splitting in perovskites. New chiral perovskites reported here couple a sizeable spin-splitting with chiral degrees of freedom and offer a unique paradigm of potential interest for spintronics.

Elucidating the origin of chiroptical activity in chiral 2D perovskites through nano-confined growth

“…This implies that the enhanced asymmetric factor of CPPL (g CPPL ) in chiral 2D OIHPs results from the facilitated chirality transfer phenomena rather than the Rashba effect itself (induced by the large SOC of OIHPs). Very recently, the Mitzi group found that the Rashba-Dresselhaus spin-splitting is a consequence of the chirality transfer phenomena 52 . Based on their findings and experimental results, the other effects such as the Rashba effect or Rashba-Dresselhaus spin-splitting (whether it occurs or not), which might contribute to the measured CPPL, cannot be explained separately.…”

Alkyl–Aryl Cation Mixing in Chiral 2D Perovskites

“…7,31 A particular application of inorganic layer asymmetry relates to Rashba−Dresselhaus spin-splitting in 2D perovskites, which may play an important role in controlling spin-related properties. 31,32 The optical properties of all 2D perovskites in this work were examined via UV−vis absorption spectroscopy (Figure 4a,c). While the pure chiral perovskite (i.e., with S/R-MePEA) exhibits a relatively blue-shifted exciton peak, the achiral perovskite (i.e., C4A) exhibits a red-shifted peak, with the exciton peak for the mixed-cation perovskite falling in between.…”

“…Fundamentally, the PbBr 6 octahedra tilting distortions arise from a complex interplay of charge-density, steric, and space-filling requirements, as well as specific hydrogen bonding interactions that couple the inorganic and organic sublattices. Chiral spacer cations always necessitate a chiral Sohncke space group to describe the overall perovskite structure; however, the degree of chirality (i.e., inversion and mirror asymmetry) in the isolated inorganic layers depends on the type and extent of specific bond angle distortions. , In the pure chiral perovskite with P 2 1 2 1 2 1 global space group, the inorganic framework comprises effectively two inorganic layers, each of which is nominally noncentrosymmetric with a P2 1 layer-symmetry (as determined by PLATON; see the Supporting Information for details) because of irregular tilting distortion of neighboring PbBr 6 octahedra within any given layer.…”

“…However, given the D 2 symmetry of the inorganic framework, the spin polarizations of these two distinct inorganic layers should nearly cancel. 32 Consequently, CD in the pure chiral perovskites may arise primarily by the mixed electric/magnetic transition dipole moment mechanism outlined above, eq 2, or via electronic interactions 37,38 between the inorganic layers and the chiral organic cations. The fact that the mixed-cation perovskite shows CD of opposite polarity and of higher magnitude than the pure chiral perovskite (despite the lower concentration of chiral organics) suggests that the CD may occur via an additional mechanism in these structures.…”

The Structural Origin of Chiroptical Properties in Perovskite Nanocrystals with Chiral Organic Ligands

“…For systems not including alkali cations, the authors have found computationally optimized geometries in close agreement (1% or better) with experimentally determined counterparts. [ 25,43–46 ] This correction is defined as a sum over pairwise atomic interactions. Importantly, the vdW radius of each element enters the TS formulation.…”