Defying Diamagnetism: Anomalous Redshift and Robust Chiral Spin Mixing in 2D Perovskites under High Magnetic Fields up to 50 T
We report circularly polarized magneto-photoluminescence (MPL) measurements on the enantiomeric pair of two-dimensional chiral perovskites R- and S-(C4H9NH3)2PbI4 in pulsed magnetic fields up to 50 T at 4.2 K. The R-form exhibits strong preferential emission into the RC channel (I_RC/I_LC = 10:1), with the S-form showing the opposite sense, robust against the applied field. Three key observations are reported: (i) an anomalous redshift of all exciton transition energies with increasing field-contrasting with the normal diamagnetic blueshift of achiral perovskites-with a non-monotonic initial blueshift to 7.6 T in the dominant RC channel of the R-form; (ii) complete invariance of PL peak positions upon reversal of the field direction, consistent with Rashba-induced mixing of the bright exciton with a nearby m_x = 0 dark state; and (iii) field-induced increase in PL intensity and narrowing of the linewidth, attributed to suppression of disorder scattering as the cyclotron orbit contracts. These results are interpreted in the framework of Rashba spin-splitting and polaron formation in the chiral two-dimensional perovskite lattice.