强自旋轨道耦合化合物Sr2-xLaxIrO4的掺杂和拉曼谱学

利用固相反应法成功制备了Sr_2-xLa_xIrO₄系列掺杂样品, 并详细研究了样品晶体结构随掺杂的演变. 拉曼散射峰向高频移动和X射线衍射谱的结构精修数据发现随着掺杂量的增加, c轴晶格常数减小, 顶角Ir–O1键键长随之减小, 表明掺杂导致晶格收缩, 而且IrO₆八面体畸变程度减弱. 变温拉曼散射谱显示随着温度降低也出现蓝移现象, 且与顶角氧相关的拉曼振动模式的蓝移在110 K附近出现明显跳变, 表明在该温度附近出现了结构变化和磁性质转变.

Doping and Raman scattering of strong spin-orbit-coupling compound Sr2-xLaxIrO4

Novel unconventional physical phenomena, such as metal-insulator transition, high temperature superconductivity, colossal magneto-resistance and quantum criticality, are usually found in transition metal oxides (TMOs) with layered perovskite structures. Great success has been achieved in 3d TMOs, in which the localized 3d states yield strongly correlated narrow bands with a large on-site Coulomb repulsion U and a small band width W. Anomalous insulating behaviors are reported in the 5d TMOs, such as Sr₂IrO₄ system, which is surprising since the 5d TMOs are usually considered as weakly correlated wide band systems with largely reduced on-site Coulomb repulsion U due to delocalized 5d states. The crystal structure of Sr₂IrO₄ consists of two-dimensional (2D) IrO₂ layers, similar to the parent compound La2CuO4 of the cuprates. Theoretically, a variational Monte Carlo study of Sr₂IrO₄ suggests that d-wave like superconductivity may appear but only within a narrow region of electron doping. In contrast, an s_±^*-wave phase is established for hole doping deduced from functional renormalization group, and triggered by spin fluctuations within and across the two conduction bands. Moreover, triplet p-wave pairing state with relatively high transition temperature emerges on the hole-doped side when the Hund's coupling is comparable to spin-orbit coupling. Several experiments are tried to search for the predicted unconventional superconductivity due to both electron-and hole-doping. However, to the best of our knowledge, it has not been found yet in the carrier-doped Sr₂IrO₄ system. Hence, more detailed studies are needed to explore the potential superconductivity.#br#A series of La doped Sr_2-xLa_xIrO₄ samples is synthesized based on solid state reaction method. The evolution of the crystal structure is studied by the X-ray diffraction, scanning electron microscopy, together with the Raman spectrum. It is found that the crystal constant of the c-axis decreases with increasing doping level as well as the apical Ir—O1 bond length, indicating the lattice construction. Moreover, the distortion of the IrO₆ octahedron reduces with increasing doping level. Therefore, blue shift occurs of the Raman scattering peaks. The temperature dependence of the Raman spectrum is also studied. It is found that the frequencies of the A_1g and B_1g vibration modes increase with temperature decreasing and an abnormal jump occurs around 110 K, which is believed to be correlated with the structural change and the magnetic transition around this temperature.