Kim Dongwook, Ahn G, Schmehr J, Wilson S D, Moon S J
Department of Physics, Hanyang University, Seoul, 04763, Republic of Korea.
Materials Department, University of California, Santa Barbara, CA, 93106, USA.
Sci Rep. 2022 Nov 8;12(1):18957. doi: 10.1038/s41598-022-23593-z.
We investigated the doping and temperature evolutions of the optical response of Sr(IrMn)O single crystals with 0 ≤ x ≤ 0.36 by utilizing infrared spectroscopy. Substitution of 3d transition metal Mn ions into SrIrO is expected to induce an insulator-to-metal transition via the decrease in the magnitude of the spin-orbit coupling and the hole doping. In sharp contrast, our data reveal the resilience of the spin-orbit coupling and the incoherent character of the charge transport. Upon Mn substitution, an incoherent in-gap excitation at about 0.25 eV appeared with the decrease in the strength of the optical transitions between the effective total angular momentum J bands of the Ir ions. The resonance energies of the optical transitions between the J bands which are directly proportional to the magnitude of the spin-orbit coupling hardly varied. In addition to these evolutions of the low-energy response, Mn substitution led to the emergence of a distinct high-energy optical excitation at about 1.2 eV which is larger than the resonance energies of the optical transitions between the J bands. This observation indicates that the Mn 3d states are located away from the Ir 5d states in energy and that the large difference in the on-site energies of the transition metal ions is responsible for the incoherent charge transport and the robustness of the spin-orbit coupling. The effect of Mn substitution was also registered in the temperature dependence of the electronic response. The anomaly in the optical response of the parent compound observed at the antiferromagnetic transition temperature is notably suppressed in the Mn-doped compounds despite the persistence of the long-range antiferromagnetic ordering. The suppression of the spin-charge coupling could be related to charge disproportionation of the Ir ions.
我们利用红外光谱研究了0≤x≤0.36的Sr(IrMn)O单晶的光学响应随掺杂和温度的变化。将3d过渡金属Mn离子替代SrIrO有望通过自旋轨道耦合强度的降低和空穴掺杂诱导绝缘体到金属的转变。然而，与预期形成鲜明对比的是，我们的数据揭示了自旋轨道耦合的弹性和电荷传输的非相干特性。Mn替代后，约0.25 eV处出现了一个非相干的能隙激发，同时Ir离子有效总角动量J带之间的光学跃迁强度降低。与自旋轨道耦合强度成正比的J带之间光学跃迁的共振能量几乎没有变化。除了低能响应的这些变化外，Mn替代还导致在约1.2 eV处出现了一个明显的高能光学激发，该激发大于J带之间光学跃迁的共振能量。这一观察结果表明，Mn 3d态在能量上远离Ir 5d态，过渡金属离子在位能上的巨大差异是电荷非相干传输和自旋轨道耦合稳健性的原因。Mn替代的影响也体现在电子响应的温度依赖性上。尽管长程反铁磁有序仍然存在，但在Mn掺杂化合物中，在反铁磁转变温度下观察到的母体化合物光学响应异常被显著抑制。自旋-电荷耦合的抑制可能与Ir离子的电荷歧化有关。
