AI 中文总结
研究混合钙钛矿纳米壁中铁弹性对称性破缺对激子态的影响，利用掠角沉积制备纳米壁并结合多种光谱技术，观察到不同温度下的激子分裂及耦合现象，揭示了铁弹性织构和相共存可改变激子-晶格耦合，实现对称选择性光学响应。
AI 中文摘要
混合金属卤化物钙钛矿是软半导体，其中电子激发受晶格畸变和结构相变强烈影响。一个重要的开放性问题是铁弹性对称性破缺仅仅拓宽光学共振还是通过激子-晶格耦合改变激子态。本文利用掠角沉积制备的高度取向MAPbI3纳米壁来解决此问题，实现铁弹性织构、结构各向异性和明确光轴之间的对称选择性耦合。结合变温光致发光、X射线衍射和偏振分辨超快瞬态吸收光谱，我们在5K的正交相中观察到偏振选择性激子分裂，其具有正交光学选择规则和45meV的能量分离。在160K附近正交相和四方相共存时，一个低能晶格耦合激发出现在各向异性分裂激子结构中心下方58meV处，与激子和晶格修饰态之间的耦合一致。在更高温度下，这些激发逐渐获得晶格修饰特征并伴有光学各向异性降低。一个对称引导的有效哈密顿量捕捉了结构转变过程中从各向异性分裂激子到耦合激子和晶格修饰态的演化。我们的结果表明铁弹性织构和相共存可以改变激子-晶格耦合，为软极性半导体中的对称选择性光学响应提供了一条途径。
英文摘要
Hybrid metal-halide perovskites are soft semiconductors in which electronic excitations are strongly influenced by lattice distortions and structural phase transitions. An important open question is whether ferroelastic symmetry breaking merely broadens optical resonances or instead modifies excitonic states through exciton-lattice coupling. Here, we address this question using highly aligned MAPbI3 nanowalls fabricated by glancing-angle deposition, enabling symmetry-selective coupling between ferroelastic texture, structural anisotropy, and a well-defined optical axis. Combining temperature-dependent photoluminescence, X-ray diffraction and polarization-resolved ultrafast transient absorption spectroscopy, we observe a polarization-selective excitonic splitting in the orthorhombic phase at 5 K, characterized by orthogonal optical selection rules and a 45 meV energy separation. Near 160 K, where orthorhombic and tetragonal phases coexist, a lower-energy lattice-coupled excitation emerges 58 meV below the centre of the anisotropically split excitonic structure, consistent with coupling between excitonic and lattice-dressed states. At higher temperatures, these excitations progressively acquire lattice-dressed character accompanied by reduced optical anisotropy. A symmetry-guided effective Hamiltonian captures the evolution from anisotropically split excitons to coupled excitonic and lattice-dressed states across the structural transition. Our results show that ferroelastic texture and phase coexistence can modify exciton-lattice coupling, providing a route to symmetry-selective optical responses in soft polar semiconductors.
Comments9 pages, 5 Figures, Supplementary Information available
