We study the effect of isoelectronic doping and external pressure in tuning the ground state of the honeycomb iridate ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ by combining optical spectroscopy with synchrotron x-ray diffraction measurements on single crystals. The obtained optical conductivity of ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ is discussed in terms of a Mott-insulating picture versus the formation of quasimolecular orbitals and in terms of Kitaev interactions. With increasing Li content $x$, $\left({\mathrm{Na}}_{1-x}{\mathrm{Li}}_x\right){}_2{\mathrm{IrO}}_3$ moves deeper into the Mott-insulating regime, and there are indications that up to a doping level of 24% the compound comes closer to the Kitaev limit. The optical conductivity spectrum of single-crystalline $\alpha \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ does not follow the trends observed for the series up to $x=0.24$. There are strong indications that $\alpha \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ is not as close to the Kitaev limit as ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ and lies closer to the quasimolecular orbital picture instead. Except for the pressure-induced hardening of the phonon modes, the optical properties of ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ seem to be robust against external pressure. Possible explanations of the unexpected evolution of the optical conductivity with isolectronic doping and the drastic change between $x=0.24$ and $x=1$ are given by comparing the pressure-induced changes of lattice parameters and the optical conductivity with the corresponding changes induced by doping.

中文翻译：

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高压对等电子掺杂对蜂窝状铱酸盐Na2IrO3的影响

我们研究了等电子掺杂和外部压力在调节蜂窝状铱酸盐的基态中的作用 ${娜}_{\mathrm{2个}}{\mathrm{氧化铁}}_3$通过将光谱学与同步加速器X射线衍射测量相结合来对单晶进行测量。所获得的光导率${娜}_{\mathrm{2个}}{\mathrm{氧化铁}}_3$关于Mott绝缘图片与准分子轨道的形成以及Kitaev相互作用进行了讨论。随着锂含量的增加 $X$， $（{娜}_{\mathrm{1个}-X}{里}_X）{}_{\mathrm{2个}}{\mathrm{氧化铁}}_3$有迹象表明，高达24％的掺杂水平使该化合物更接近Kitaev极限。单晶的光导谱$\alpha \text{-}{里}_{\mathrm{2个}}{\mathrm{氧化铁}}_3$ 一直未遵循该系列所观察到的趋势 $X=0.24$。有强烈的迹象表明$\alpha \text{-}{里}_{\mathrm{2个}}{\mathrm{氧化铁}}_3$ 没有像Kitaev极限那么近 ${娜}_{\mathrm{2个}}{\mathrm{氧化铁}}_3$而是更靠近准分子轨道图片。除了压力引起的声子模态硬化外，光学性质${娜}_{\mathrm{2个}}{\mathrm{氧化铁}}_3$似乎可以抵抗外部压力。等电子掺杂引起的光电导率意外演变和两者之间的急剧变化的可能解释。$X=0.24$ 和 $X=\mathrm{1个}$ 通过比较压力引起的晶格参数变化和光导率与掺杂引起的相应变化来给出。