We study the exciton states in the symmetrically biased dice model, the electronic structures of which have an isolated flat band between two dispersive bands. At 1/3 or 2/3 filling, the model describes a two-dimensional semiconductor with the band edge at two degenerate valleys. Because of qualitative changes in the eigenvectors resulting from the bias term, the interband transition between the flat band and a dispersive band is valley contrasting under circularly polarized light. In terms of an effective-mass model and a realistic electron-hole interaction, we numerically calculate the spectrum and wave functions of the intravalley excitons, which are treated as Wannier-Mott excitons. We also discuss the fine structures of the exciton spectrum induced by the intravalley and intervalley exchange interactions. The symmetrically biased dice model thereby proves to be a new platform for valley-contrasting optoelectronics.

中文翻译：

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对称偏置骰子模型中的谷对比带间跃迁和激子

我们研究了对称偏置骰子模型中的激子态，其电子结构在两个色散带之间有一个孤立的平坦带。在 1/3 或 2/3 填充时，该模型描述了一个二维半导体，其带边位于两个简并谷。由于偏置项导致本征向量发生质的变化，在圆偏振光下，平带和色散带之间的带间过渡是谷对比。在有效质量模型和现实的电子-空穴相互作用方面，我们数值计算了谷内激子的光谱和波函数，它们被视为 Wannier-Mott 激子。我们还讨论了由谷内和间隔交换相互作用引起的激子光谱的精细结构。