标题： Ba$_2$CaOsO$_6$中铁八极序的可能性通过X射线磁性二色性测量进行评估 显示英文标题

标题： Possibility of ferro-octupolar order in Ba$_2$CaOsO$_6$ assessed by X-ray magnetic dichroism measurements

摘要： 局域化的$5d^2$电子在立方晶场中具有如电四极子和磁八极子等多极矩。 我们通过X射线吸收谱（XAS）和X射线磁圆二色谱（XMCD）在Os$L_{2,3}$边缘研究了含有Os$^{6+}$ ($5d^2$) 离子的立方双钙钛矿Ba$_2$CaOsO$_6$，该物质在低于$T^* \sim$ 50 K时表现出向“隐藏序”的相变。 锇$5d$的$t_{2g}$和$e_g$能级之间的立方配位场分裂通过XAS被推断为$\sim$4 eV。 XMCD光谱的温度依赖性与最低$\sim$18 meV剩余立方分裂一致，将$J_{\rm eff} =$2多重态分裂为非-Kramers$E_g$双重态基态和$T_{2g}$三重态激发态。 在虚构的强磁场下的配体场（LF）多重态计算表明，如果在“隐藏有序”状态下稳定铁八极序，则最近邻八极之间的交换相互作用应强达$\sim$1.5 meV，这与之前通过模型和密度泛函理论计算理论上预测的$\sim$1 meV交换相互作用一致。 显示英文摘要

摘要： Localized $5d^2$ electrons in a cubic crystal field possess multipoles such as electric quadrupoles and magnetic octupoles. We studied the cubic double perovskite Ba$_2$CaOsO$_6$ containing the Os$^{6+}$ ($5d^2$) ions, which exhibits a phase transition to a `hidden order' below $T^* \sim$ 50 K, by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at the Os $L_{2,3}$ edge. The cubic ligand-field splitting between the $t_{2g}$ and $e_g$ levels of Os $5d$ was deduced by XAS to be $\sim$4 eV. The temperature dependence of the XMCD spectra was consistent with a $\sim$18 meV residual cubic splitting of the lowest $J_{\rm eff} =$ 2 multiplet state into the non-Kramers $E_g$ doublet ground state and the $T_{2g}$ triplet excited state. Ligand-field (LF) multiplet calculation under fictitious strong magnetic fields indicated that the exchange interaction between nearest-neighbor octupoles should be as strong as $\sim$1.5 meV if a ferro-octupole order is stabilized in the `hidden-ordered' state, consistent with the exchange interaction of $\sim$1 meV previously predicted theoretically using model and density functional theory calculations.