Two-dimensional organic-inorganic perovskites have garnered great attention due to their strong spin-orbit coupling and quantum confinement effects arising from their layered structures. These materials hold promising applications in optoelectronics, photovoltaics, and spintronic devices. The photogenerated carrier dynamics in two-dimensional perovskites strongly depend on the complex interactions between carriers and lattice vibrations. However, the electroacoustic interaction and its role in spin relaxation have yet to be widely explored.
Associate Professor Xihan Chen’s research group from the Department of Mechanical and Energy Engineering (MEE) at the Southern University of Science and Technology (SUSTech) has made significant progress in the study of carrier spin polarization properties in organic-inorganic semiconductor (4AMP) PbI₃.
Their findings, titled “Giant deformation potential induced small polaron effect in Dion–Jacobson two-dimensional lead halide perovskites”, have been published in the journal National Science Review.
The researchers utilized ultrafast spectroscopy to investigate carrier spin dynamics and electroacoustic coupling properties in the organic-inorganic semiconductor (4AMP)(MA)ₙ₋₁PbnI₃ₙ₊₁ (4AMP = 4-(aminomethyl)piperidinium, n=1-3). They employed ultrafast circularly polarized light to selectively excite pure spin states. Femtosecond laser pulses with either the same or opposite circular polarization were used to probe the decay or growth of spin-polarized signal. This allowed them to obtain spin relaxation dynamics.
Their findings revealed that the formation of small polarons significantly enhances the spin polarization lifetime. The study also used ultrafast optical coherent phonon dynamics, optical Kerr spectroscopy, and first-principles calculations. These techniques helped observe the formation of small polarons, each with sizes of approximately two lattice units.
Figure 1. Spin dynamics and small polaron formation in Dion–Jacobson two-dimensional perovskites
The team also revealed that Dion–Jacobson type perovskites exhibit significant lattice distortion due to unique hydrogen bonding interactions, suggesting strong carrier-phonon interactions in these materials. This electroacoustic interaction strength can be characterized by the deformation potential parameter. The formation of small polarons is driven by a giant deformation potential as large as −123 eV, approximately 30 times greater than that in conventional perovskite materials.
Figure 2. Lattice distortion promotes small polaron formation
Lattice thermal vibrations are significantly affected by temperature, with carrier-lattice interactions weakening as the temperature decreases. The monotonic temperature dependence of coherent phonon and spin relaxation lifetimes suggests that the carrier-phonon coupling mechanism dominates spin relaxation. This finding highlights the key role of small polaron formation in suppressing spin depolarization.
Figure 3. Temperature effect on carrier-phonon interaction
Doctoral students Yuling Huang and Shaokuan Gong from the Department of MEE at SUSTech and master’s student Qianxia Chen from the School of Physics at South China Normal University (SCNU) are the co-first authors of this paper. Associate Professor Xihan Chen and Associate Researcher Jin-Zhu Zhao from SCNU are the co-corresponding authors, with SUSTech serving as the first affiliated institution.
Paper link: https://academic.oup.com/nsr/advance-article/doi/10.1093/nsr/nwae461/7925867
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