Ahn Gihyeon, Schmehr J L, Porter Z, 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. 2020 Dec 18;10(1):22340. doi: 10.1038/s41598-020-79263-5.
We report on optical spectroscopic study of the Sr(IrRu)O system over a wide doping regime. We find that the changes in the electronic structure occur in the limited range of the concentration of Ru ions where the insulator-metal transition occurs. In the insulating regime, the electronic structure associated with the effective total angular momentum J = 1/2 Mott state remains robust against Ru doping, indicating the localization of the doped holes. Upon entering the metallic regime, the Mott gap collapses and the Drude-like peak with strange metallic character appears. The evolution of the electronic structure registered in the optical data can be explained in terms of a percolative insulator-metal transition. The phonon spectra display anomalous doping evolution of the lineshapes. While the phonon modes of the compounds deep in the insulating and metallic regimes are almost symmetric, those of the semiconducting compound with x = 0.34 in close proximity to the doping-driven insulator-metal transition show a pronounced asymmetry. The temperature evolution of the phonon modes of the x = 0.34 compound reveals the asymmetry is enhanced in the antiferromagnetic state. We discuss roles of the S = 1 spins of the Ru ions and charge excitations for the conspicuous lineshape asymmetry of the x = 0.34 compound.
我们报告了在宽掺杂范围内对Sr(IrRu)O体系的光学光谱研究。我们发现，电子结构的变化发生在Ru离子浓度的有限范围内，此时会发生绝缘体-金属转变。在绝缘状态下，与有效总角动量J = 1/2的莫特态相关的电子结构对Ru掺杂保持稳健，表明掺杂空穴的局域化。进入金属状态后，莫特能隙崩塌，出现具有奇异金属特性的德鲁德样峰。光学数据中记录的电子结构演变可以用渗流绝缘体-金属转变来解释。声子谱显示出线形的反常掺杂演变。虽然处于绝缘和金属状态深处的化合物的声子模式几乎是对称的，但靠近掺杂驱动的绝缘体-金属转变的x = 0.34的半导体化合物的声子模式显示出明显的不对称性。x = 0.34化合物的声子模式的温度演变表明，在反铁磁状态下不对称性增强。我们讨论了Ru离子的S = 1自旋和电荷激发对x = 0.34化合物明显的线形不对称性的作用。
