Decoupling of the antiferromagnetic and insulating states in Tb-doped Sr2IrO4
Decoupling of the antiferromagnetic and insulating states in Tb-doped Sr2IrO4
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DOI：
10.1103/physrevb.92.214411
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发表时间：
2015-11
影响因子：
3.7
通讯作者：
Jinchen Wang;Jinchen Wang;Jinchen Wang;S. Aswartham;F. Ye;F. Ye;J. Terzic;Hao Zheng;D. Haskel-D.-Has
中科院分区：
文献类型：
--
作者：
Jinchen Wang;Jinchen Wang;Jinchen Wang;S. Aswartham;F. Ye;F. Ye;J. Terzic;Hao Zheng;D. Haskel-D.-Has
$\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$是具有反铁磁跃迁的自旋-轨道耦合绝缘体，在${T}_{N}=240\phantom{\rule{0.16em}{0ex}}\mathrm{K}$处。我们报告了单晶$\mathrm{S}{\mathrm{r}}_{2}\mathrm{I}{\mathrm{r}} {1\ enthrm {-}x}\mathrm{T}{\mathrm{b}} {x}{\mathrm{O}} {4}\phantom{\rule{0.16em}{0ex}}(0\ensuremath{\le}x\ensuremath{\le}0.03)$的综合研究结果。本研究发现，仅3%的$(x=0.03)$四价$\mathrm{T}{\mathrm{b}}^{4+}(4{\mathrm{f}}^{7})$取代$\mathrm{I}{\mathrm{r}}^{4+}$（而不是$\mathrm{S}{\mathrm{r}}^{2+}$）完全抑制了长程共线AFM跃迁，但保留了绝缘状态，导致磁相互作用和电荷间隙解耦的相图。在$x=0.03$处的绝缘态的特点是低温比热异常大，中子衍射的磁峰在（0.95,0,0）和（0,0.95,0）处存在不匹配的磁态，表明其为螺旋或自旋密度波序。可见，Tb掺杂有效地改变了自旋轨道相互作用（SOI）和四方晶体电场的相对强度，增强了与SOI竞争的洪德规则耦合，使AFM态不稳定。然而，AFM的消失并不伴随着金属态，这主要是因为Ir和Tb位点的能级不匹配削弱了载流子跳变，导致了持久的绝缘状态。这项工作强调了AFM和绝缘状态之间的非常规相关性，其中磁跃迁在铱酸盐中电荷间隙的形成中没有关键作用。
$\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ is a spin-orbit-coupled insulator with an antiferromagnetic (AFM) transition at ${T}_{N}=240\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. We report results of a comprehensive study of single-crystal $\mathrm{S}{\mathrm{r}}_{2}\mathrm{I}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{T}{\mathrm{b}}_{x}{\mathrm{O}}_{4}\phantom{\rule{0.16em}{0ex}}(0\ensuremath{\le}x\ensuremath{\le}0.03)$. This study found that a mere 3% $(x=0.03)$ of tetravalent $\mathrm{T}{\mathrm{b}}^{4+}(4{\mathrm{f}}^{7})$ substituting for $\mathrm{I}{\mathrm{r}}^{4+}$ (rather than $\mathrm{S}{\mathrm{r}}^{2+}$) completely suppresses the long-range collinear AFM transition but retains the insulating state, leading to a phase diagram featuring a decoupling of the magnetic interactions and charge gap. The insulating state at $x=0.03$ is characterized by an unusually large specific heat at low temperatures and an incommensurate magnetic state having magnetic peaks at (0.95,0,0) and (0,0.95,0) in the neutron diffraction, suggesting a spiral or spin-density-wave order. It is apparent that Tb doping effectively changes the relative strength of the spin-orbit interaction (SOI) and the tetragonal crystal electric field and enhances the Hund's rule coupling that competes with the SOI, and destabilizes the AFM state. However, the disappearance of the AFM is accompanied by no metallic state chiefly because an energy level mismatch for the Ir and Tb sites weakens charge carrier hopping and causes a persistent insulating state. This work highlights an unconventional correlation between the AFM and insulating states in which the magnetic transition plays no critical role in the formation of the charge gap in the iridate.