标题： 类分子态的三聚体铱酸钡 Ba$_4$NbIr$_3$O$_{12}$ 显示英文标题

标题： Quasimolecular electronic structure of the trimer iridate Ba$_4$NbIr$_3$O$_{12}$

摘要： 绝缘的混合价态 Ir$^{+3.66}$化合物 Ba$_4$NbIr$_3$O$_{12}$每个 Ir$_3$O$_{12}$三聚体单元包含两个空穴。 我们通过在 Ir$L_3$边缘的共振非弹性 X 射线散射 (RIXS) 和精确对角化来研究电子结构。 这些空穴占据在三聚体上离域的准分子轨道。 这导致了一个丰富的内部$t_{2g}$激发谱，其范围从0.5 eV扩展到大于2 eV的能量。 此外，它作为传递动量 q 的函数，产生了强烈的RIXS强度调制。 准分子三聚体特征的明显指纹是观察到两个调制周期，$2\pi/d$和$2\pi/2d$，其中 d 和 2d 表示三聚体内的Ir-Ir距离。 我们讨论了特定的调制如何反映激发态波函数的特性。 我们的定量分析表明，约0.4 eV的自旋-轨道耦合$\lambda$对电子态的特性至关重要，尽管有约0.8 eV的较大跃迁$t_{a_{1g}}$。 单个三聚体的基态由两个空穴占据成键 j=1/2 轨道很好地描述，形成 J=0 的消失准分子磁矩。 显示英文摘要

摘要： The insulating mixed-valent Ir$^{+3.66}$ compound Ba$_4$NbIr$_3$O$_{12}$ hosts two holes per Ir$_3$O$_{12}$ trimer unit. We address the electronic structure via resonant inelastic x-ray scattering (RIXS) at the Ir $L_3$ edge and exact diagonalization. The holes occupy quasimolecular orbitals that are delocalized over a trimer. This gives rise to a rich intra-$t_{2g}$ excitation spectrum that extends from 0.5 eV to energies larger than 2 eV. Furthermore, it yields a strong modulation of the RIXS intensity as a function of the transferred momentum q. A clear fingerprint of the quasimolecular trimer character is the observation of two modulation periods, $2\pi/d$ and $2\pi/2d$, where d and 2d denote the intratrimer Ir-Ir distances. We discuss how the specific modulation reflects the character of the wavefunction of an excited state. Our quantitative analysis shows that spin-orbit coupling $\lambda$ of about 0.4 eV is decisive for the character of the electronic states, despite a large hopping $t_{a_{1g}}$ of about 0.8 eV. The ground state of a single trimer is described very well by both holes occupying the bonding j=1/2 orbital, forming a vanishing quasimolecular moment with J=0.