Signature of a pressure-induced dynamic state in Cu-based hybrid perovskite

초록

In transition-metal systems, the Jahn-Teller (JT) framework governs local symmetry and structure-property relations via vibronic coupling between electronic states and lattice vibrations, inducing symmetry-lowering distortions. The static JT model is robust, but becomes insufficient when high average symmetry coexists with local distortions. This necessitates the dynamic JT concept, in which local distortions fluctuate among symmetry-related states and apparent symmetry depends on averaging. Cu-based hybrid perovskites are typically interpreted within the static JT framework; however, their behavior under compression remains incompletely understood as the octahedral environment evolves toward higher symmetry. Here, we study (C8H12N)2CuCl4 using combined high-pressure spectroscopic, diffraction, and computational approaches. The results reveal that pressure-driven JT evolution cannot be captured by a single static model, but proceeds through an intermediate regime at 4-8 GPa. In this regime, the combined results support a dynamic JT contribution, with local Cu-Cl configurations fluctuating despite a strongly reduced static distortion. Spectral broadening, peak convergence, modified d-d absorption and band gap narrowing support this interpretation. Consequently, the material exhibits an apparently simplified average structure, even though spectroscopic response retains pronounced local JT complexity. This work demonstrates that pressure-tuned competition between static distortions and dynamic vibronic averaging provides a framework for interpreting structure-spectroscopy correlations and functionality.

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