Jahn-Teller Effect Dominates the Left-Hand Rule: Magneto-Optics in Metal Halide Lattice

Symmetry operation during molecular packing in the crystalline phase determines diverse unique features. Inducing asymmetry in hybrid inorganic-organic metal-halide typically relies on importing chiral A-site cations or exploiting hydrogen bonding to distort the lattice. However, achieving precise spatial control over asymmetrical molecules using stereo-chemical templating strategy remains challenging. Here, we demonstrate that two highly symmetric single crystals, DMA₄InCl₇:Sb³⁺ and DETABiCl₆:Sb³⁺, containing isolated SbCl₆ octahedra with idealized octahedral (O_h) geometry, exhibit a unique case of a static Jahn-Teller effect (JTE) with the interplay of strong spin-orbit coupling interaction. This inherently handed property drives the spontaneous lowering of symmetry from O_h to D_4h, accompanied by structural deformation in the excited states. Under an external magnetic field (B from 0 to 45 T) applied parallel or anti-parallel to the (100) direction, the A_2u level in the upper position is preferentially populated during relaxation, resulting in a dominant left-circularly polarized (σ-) emission. Rather than forming an intrinsically asymmetric lattice at equilibrium, chiral preference emerges from a Jahn-Teller-amplified transient-state process, yielding a highly effective g_m value of up to 8.9×10^-2. This mechanism will be broadly applicable to d- and p-block metal-activated hybrid metal halides across various dimensionalities.