Rashba band splitting in two-dimensional Ruddlesden–Popper halide perovskites

Abstract

Due to the presence of heavy elements and the dynamic nature of hybrid halide perovskites, the strong spin–orbit coupling effect can give rise to Rashba band splitting in these materials. Despite many reports on the Rashba effect in 3D perovskites like CH3NH3PbI3, little is known about its presence in two-dimensional Ruddlesden–Popper (2DRP) perovskites. In this work, we use first-principle calculations to investigate the magnitude and origin of the Rashba effect in three families of 2DRP perovskites. We demonstrate the correlation between the splitting magnitude and the octahedron distortions. Moreover, different numbers of inorganic layers, spacer cations, and A-site cations have a great influence on the Rashba splitting through different mechanisms. While structures with C6H5C2H4NH3 (PEA) have a significant Rashba splitting only in the monolayer condition, C4H9NH3 (BA) induces large distortion by tilting the CH3NH3 (MA) cations around all octahedrons, giving rise to a larger Rashba splitting with an increasing number of inorganic layers. Our work elucidates the magnitude and origin of the Rashba splitting in 2DRP perovskites and provides guidelines for the manipulation of the Rashba splitting in these materials.

The Rashba effect in two-dimensional hybrid perovskites: the impacts of halogens and surface ligands

“…Through the results it is also indicated that the impacts of tert -BA on the Rashba splitting are more insensitive toward the thickness changing since the surface distortion degree induced by tert -BA does not change obviously with the thickness increasing (Δ θ Br = 14.0°–17.8°), and the splitting energy E R is approximately 50 meV except the 3L model. The overall trend is similar to that previously reported in 2D MAPbI 3 , 17,36 yet without obvious oscillations. The α R values are shown in Fig.…”

“…A theoretical study has discussed the Rashba effect in 2D MAPbI 3 , which has proposed that the distortion degree of the [PbI 6 ] − octahedron is responsible for the magnitude of the Rashba splitting. 36 Consequently, these inconsistent reports indicate that the research about the Rashba effect in 2D HOIPs is still insufficient at present.…”

Understanding of Layer-Dependent Stability and Rashba Spin Splitting of Two-Dimensional Organic–Inorganic Halide Perovskites α-FABX3 (B = Ge, Sn, and Pb; X = Cl, Br, and I)

“…On the other hand, the perturbative Hamiltonian of the Rashba effect can be expressed as H R = α R ( k x σ y – k y σ x ), and then the energy dispersion relation should be corrected as . In nearly free electron approximation, the Rashba parameter α R = 2 E 0 / k 0 is used to measure the magnitude of the Rashba effect, in which E 0 is the Rashba energy and k 0 is the k -space shift. As shown in Figure f, the calculated Rashba parameters of 2D α-FAPbI 3 (one to four layers) are 1.42, 1.58, 1.29, and 1.22 eV·Å, respectively, and we can see that the splitting first increases (one to two layers) and then decreases (two to four layers) with thickness.…”

Structural Dimensionality Dependence of the Band Gap in An+1BnX3n+1 Ruddlesden–Popper Perovskites: A Global Picture

“…The capability of the PBEsol functional to provide an accurate description of band gap evolution has also been demonstrated in previous works on chalcogenides, 28 oxides, 13 and halides. 2 More accurate band gap values could be obtained by using a hybrid functional 17,29 and including the effect of spin−orbit coupling, 16,17,29,30 van der Waals forces, 31 and the Rashba effect, 31,32 while they will not affect band gap evolution according to previous works. 16,17,29−31 The excellent agreement of band gap evolution for several representative compounds between PBEsol and Heyd−Scuseria−Ernzerhof (HSE06) screened hybrid functionals 33 (see Figure S1) further confirms that the PBEsol functional can provide a quantitative comparison of band gap evolution.…”