Two-dimensional monolayer structures of transition metal dichalogenides (TMDs) have been shown to allow many higher-order excitonic bound states, including trions (charged excitons), biexcitons (excitonic molecules), and charged biexcitons. We report here experimental evidence and the theoretical basis for a new bound excitonic complex, consisting two free carriers bound to an exciton in a bilayer structure. Our experimental measurements on structures made using two different materials show a new spectral line at the predicted energy with two different TMD materials (MoSe₂ and WSe₂) with both n- and p-doping if and only if all the required theoretical conditions for this complex are fulfilled, in particular, only in the presence of a parallel metal layer that significantly screens the repulsive interaction between the like-charge carriers. Because these four-carrier bound states are charged bosons, they could eventually be the basis for a new path to superconductivity without Cooper pairing.

中文翻译：

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具有强金属屏蔽的双层结构中由费米子制成的带电玻色子

已证明过渡金属二卤化物 (TMD) 的二维单层结构允许许多高阶激子束缚态，包括三元（带电激子）、双激子（激子分子）和带电双激子。我们在这里报告了新的束缚激子复合物的实验证据和理论基础，该复合物由两个自由载流子以双层结构与激子结合。我们对使用两种不同材料制成的结构进行的实验测量显示了在预测能量下使用两种不同 TMD 材料（MoSe ₂和 WSe _2）的新谱线) 具有 n 和 p 掺杂，当且仅当满足该复合物的所有所需理论条件，特别是仅在平行金属层存在的情况下，该金属层显着屏蔽了类似电荷载流子之间的排斥相互作用。由于这些四载流子束缚态是带电玻色子，因此它们最终可能成为没有库珀配对的超导新路径的基础。