Abstract We establish a simple quantitative criterium for the search of new dielectric materials with high values of refractive index in the visible range. It is demonstrated, that for light frequencies below the bandgap, the latter is determined by the dimensionless parameter η calculated as the ratio of the sum of the widths of conduction and valence bands and the bandgap. Small values of this parameter, which can be achieved in materials with almost flat bands, lead to dramatic increase of the refractive index. We illustrate this rule with a particular example of rhenium dichalcogenides, for which we perform ab initio calculations of the band structure and optical susceptibility and predict the values of the refractive index n > 5 $n{ >}5$ in a wide frequency range around 1 eV together with comparatively low losses. Our findings open new perspectives in search for the new high-index/low-loss materials for all-dielectric nanophotonics.

中文翻译：

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二硒化铼的高折射率和极端双轴光学各向异性在全介电纳米光子学中的应用

摘要 我们建立了一个简单的定量标准，用于寻找在可见光范围内具有高折射率的新型介电材料。结果表明，对于带隙以下的光频率，后者由无量纲参数 η 确定，该参数计算为导带和价带宽度之和与带隙之比。该参数的较小值（可以在具有几乎平坦带的材料中实现）导致折射率的显着增加。我们用铼二硫属化物的一个特定例子来说明这个规则，为此我们对带结构和光学磁化率进行了从头计算，并预测了折射率 n > 5 $n{ >}5$ 在大约1 eV 以及相对较低的损耗。