标题： Kitaev候选材料Cu$_2$IrO$_3$绝缘态的起源 显示英文标题

标题： Origin of the insulating state in the Kitaev candidate Cu$_2$IrO$_3$

摘要： 通过晶体对称性分析和密度泛函理论计算，我们揭示了在蜂窝状Kitaev材料Cu$_2$IrO$_3$中报道的意外绝缘行为的可能微观起源。 我们的研究表明，这种材料中存在Ir离子的电荷有序不稳定性，磁性Ir$^{4+}$离子和非磁性Ir$^{3+}$离子在蜂窝晶格上交替排列。 在这种情况下，耦合磁性Ir$^{4+}$离子的次近邻相互作用形成一个扩大的三角晶格，而不是预期的蜂窝晶格。 位于铱蜂窝空位中心的磁性Cu$^{2+}$离子也形成一个三角晶格，并且还对系统的磁化做出贡献。 相互穿透的 Ir$^{4+}$ 和 Cu$^{2+}$ 三角晶格呈现出一种由两种磁性离子组成的新型蜂窝状 Kitaev 晶格。 显示英文摘要

摘要： Through a combination of crystal symmetry analysis and density functional theory calculations we unveil a possible microscopic origin of the unexpected insulating behavior reported in the honeycomb Kitaev material Cu$_2$IrO$_3$. Our study suggests that this material hosts an instability towards charge ordering of the Ir ions, with alternating magnetic Ir$^{4+}$ and non-magnetic Ir$^{3+}$ ions arranged on the honeycomb lattice. In this case, the next-nearest-neighbor interactions that couple magnetic Ir$^{4+}$ ions form an enlarged triangular lattice, instead of the expected honeycomb lattice. The magnetic Cu$^{2+}$ ions located at the centre of the iridium honeycomb voids also form a triangular lattice, and additionally contribute to the magnetization of the system. Together, the interpenetrated Ir$^{4+}$ and Cu$^{2+}$ triangular lattices present a novel type of honeycomb Kitaev lattice composed of two types of magnetic ions.