标题： 弱磁性反铁磁性和莫特绝缘体LaTiO$_3$中的轨道无序 显示英文标题

标题： Fragile altermagnetism and orbital disorder in Mott insulator LaTiO$_3$

摘要： 基于从头计算，我们证明一种莫特绝缘体LaTiO$_3$ (LTO)，此前未被检查为反铁磁材料，表现出反铁磁体的特征，即(i)完全补偿的反铁磁性和(ii)在没有自旋-轨道耦合的情况下，$\mathbf{k}$-依赖的自旋分裂电子带。 LTO的交替磁性基态由晶体对称性保护，并且特定有序的Ti离子的$d$轨道具有轨道动量$l=2.$。当单元胞中的Ti对位被单个电子占据时，每个位点具有$m=-1,s_{z}=+1/2$和$m=+1,s_{z}=-1/2$，其中$m$和$s_{z}-$分别是轨道动量和自旋的$z-$分量。通过在Green函数方法中进一步模拟轨道无序，我们揭示了其对自旋分裂的破坏性以及由此产生的交替磁性。 当每个Ti位点的单电子自旋极化态几乎由两个或三个$t_{2g}$轨道贡献时，LTO变为反铁磁性。 讨论了自旋-轨道耦合的影响，这可能导致轨道无序并抑制交替磁性。 显示英文摘要

摘要： Based on ab initio calculations, we demonstrate that a Mott insulator LaTiO$_3$ (LTO), not inspected previously as an altermagnetic material, shows the characteristic features of altermagnets, i.e., (i) fully compensated antiferromagnetism and (ii) $\mathbf{k}$-dependent spin-split electron bands in the absence of spin-orbit coupling. The altermagnetic ground state of LTO is protected by the crystal symmetry and specifically ordered $d$-orbitals of Ti ions with the orbital momentum $l=2.$ The altermagnetism occurs when sites of Ti pair in the unit cell are occupied by single electrons with $m=-1,s_{z}=+1/2$ and $m=+1,s_{z}=-1/2$ per site, with $m$ and $s_{z}-$ being the $z-$ component of the orbital momentum and spin, respectively. By further simulating orbital disorder within the Green's function method, we disclose its damaging character on the spin splitting and the resulting altermagnetism. When the single-electron spin-polarized state at each Ti site is contributed almost equally by two or three $t_{2g}$ orbitals, LTO becomes antiferromagnetic. The effect of the spin-orbit coupling, which can cause orbital disorder and suppress altermagnetism, is discussed.