反铁磁材料AgCrP2S6中的局域激子与激子-声子耦合
Localized Excitons and Exciton-Phonon Coupling in Antiferromagnetic AgCrP2S6
浏览论文内容
中文总结 AI 辅助
研究确定反铁磁材料AgCrP2S6的结构与激子性质，发现其低能激发为局域弗伦克尔激子，明确了激子-声子耦合通道，揭示其处于局域激子 regime的机制。
中文摘要 AI 辅助
AgCrP2S6兼具低对称性硫磷酸盐骨架、反铁磁Cr亚晶格与非磁性Ag位点，为低能光学响应中共价性与磁局域性的竞争提供了研究场景。我们结合单晶X射线衍射、拉曼光谱、晶格动力学计算及自洽顶点修正费曼图多体方法，确定了体相AgCrP2S6的结构、电子与激子性质。该材料在100至300K间保持单斜结构，低温下可观测到额外的Ag位点无序，优化后的结构具有动力学稳定性。多体计算显示其准粒子带隙较Cr三卤化物更小，但最低激子仍以局域为主：计算得到的低能（~1.4 eV）激发簇最适合描述为弱亮、强各向异性的弗伦克尔激子，具有主导的 onsite d-d特征及显著的配体辅助d-p混合。C2h对称性分析表明该态主要为Bu对称性，并将其主导的激子-声子耦合通道限制为Ag对角重整化与Bg介导的亮暗混合。这些结果表明，与更离子性的Cr三卤化物相比，AgCrP2S6中更强的p-d杂化缩小了准粒子带隙，而反铁磁交换与Ag位点稀释不利于强离域低能激子相关的位点间相干性，使该材料处于局域激子 regime。
英文摘要
AgCrP2S6 combines a low-symmetry thiophosphate framework with an antiferromagnetic Cr sublattice and nonmagnetic Ag sites, providing a setting in which covalency and magnetic localization compete in the low-energy optical response. We combine single-crystal x-ray diffraction, Raman spectroscopy, lattice-dynamical calculations, and self-consistent vertex corrected Feynman diagrammatic many-body approaches to determine the structural, electronic, and excitonic properties of bulk AgCrP2S6. The material remains monoclinic between 100 and 300 K, with additional Ag-site disorder resolved at low temperature, and the optimized structure is dynamically stable. The many-body calculations yield a reduced quasiparticle gap relative to Cr trihalides, but the lowest excitons remain predominantly local: the calculated low-energy (~1.4 eV) excitation cluster is best described as a weakly bright, strongly anisotropic Frenkel exciton with dominant onsite d-d character and substantial ligand-assisted d-p admixture. Symmetry analysis in the C2h setting identifies this state as predominantly Bu and constrains its leading exciton-phonon coupling channels to Ag diagonal renormalization and Bg-mediated bright-dark mixing. These results place AgCrP2S6 in a localized excitonic regime in which the stronger p-d hybridization, relative to the more ionic Cr trihalides, narrows the quasiparticle gap, while the antiferromagnetic exchange and Ag-site dilution disfavor the intersite coherence associated with strongly delocalized low-energy excitons.
