交替磁体CsCr$_2$S$_2$O中的轨道选择性莫特转变与关联放大的电荷有序

中文摘要 AI 辅助

交替磁体CsCr$_2$S$_2$O会发生由晶格畸变驱动的类Verwey金属-绝缘体转变（MIT），以及Cr亚晶格上的条纹电荷有序，这与Fe$_3$O$_4$的物理现象类似，但原子畸变仅发生在配体位点而非Cr位点，因此Cr位点间这种显著电荷失衡的驱动机制仍是谜团。利用DFT+DMFT计算，我们识别出轨道选择性莫特转变，该转变使关联金属性的$d_{yz}$轨道主导低能物理过程；我们证明S位点畸变通过Cr-$d_{yz}$与S-$p$轨道杂化，在Cr位点间触发初始微小电荷不对称，关键是这种不对称会被动态电子关联显著放大，导致不同Cr位点的Cr-$d_{yz}$轨道电荷与电子关联出现巨大差异，进一步引发交替磁体态中局域自旋极化的显著分化，最终驱动MIT。相反，我们预测将S替换为Te会削弱这种关联放大效应，因电子关联更弱而无法引发MIT。我们的发现表明，多体效应可大幅放大配体不稳定性，重塑交替磁体的电子结构，凸显配体工程对实现稳健金属性交替磁性至关重要。

英文摘要

Altermagnet CsCr$_2$S$_2$O undergoes a Verwey-type metal-to-insulator transition (MIT), accompanied by a lattice distortion and stripe charge order on the Cr sublattice. Intriguingly, the atomic distortions occur exclusively at the ligand sites rather than the Cr sites, leaving the origin of the pronounced Cr charge disproportionation unresolved. Using density functional theory plus dynamical mean-field theory (DFT+DMFT) calculations, we identify an orbital-selective Mott state in which the correlated metallic $d_{yz}$ orbital governs the low-energy physics. We show that S-site distortions produces only a small bare charge asymmetry between the Cr sublattices through Cr-$d_{yz}$--S-$p$ hybridization. Dynamical electronic correlations, however, dramatically amplify this asymmetry, producing pronounced differentiation in both the charge occupancy and correlation strength of the $d_{yz}$ orbitals. The resulting site-dependent spin polarization ultimately drives the MIT. In contrast, replacing S with Te substantially weakens this correlation-amplification effect and preserves a metallic state. Our work reveals a hidden, correlation-amplified feedback loop between ligand instabilities and electronic symmetry breaking in this altermagnetic family, highlighting ligand engineering as an effective route toward robust metallic altermagnetism.

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5 pages, 4 figures