Evidence for equilibrium exciton condensation in monolayer WTe2
Evidence for equilibrium exciton condensation in monolayer WTe2
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DOI：
10.1038/s41567-021-01427-5
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发表时间：
2021-12-23
期刊：
影响因子：
19.6
通讯作者：
Cobden, David H.
中科院分区：
文献类型：
--
作者：
Sun, Bosong;Zhao, Wenjin;Cobden, David H.
我们提供的证据表明，单层WTe2的二维主体包含由库仑引力(激子)约束的电子和空穴，这些电子和空穴在热平衡时自发形成。从室温冷却到100K时，电导率与静电掺杂呈V型关系，而化学势在中性点发展一个台阶。这些特征比独立电子图像中可能的要清晰得多，但如果电子和空穴强烈相互作用并处于平衡状态，它们可以被解释。根据第一性原理的计算表明，激子结合能大于100 meV，半径小于4 nm，这解释了它们是在高温和掺杂水平下形成的。在100K以下，观察到更强的绝缘行为，这表明形成了电荷有序状态。在激子绝缘体图像中观察到的这种状态下没有电荷密度波是令人惊讶的，但我们表明这可以用激子波函数的对称性来解释。因此，除了作为一种拓扑绝缘体，单层WTe2还在很宽的温度范围内表现出很强的相关性。激子凝聚已经在各种三维(3D)材料中观察到。现在，单层WTe2--一种2D拓扑绝缘体--也显示了这种现象。强的电子相互作用允许激子在高温下形成和凝聚。
We present evidence that the two-dimensional bulk of monolayer WTe2 contains electrons and holes bound by Coulomb attraction-excitons-that spontaneously form in thermal equilibrium. On cooling from room temperature to 100 K, the conductivity develops a V-shaped dependence on electrostatic doping, while the chemical potential develops a step at the neutral point. These features are much sharper than is possible in an independent-electron picture, but they can be accounted for if electrons and holes interact strongly and are paired in equilibrium. Our calculations from first principles show that the exciton binding energy is larger than 100 meV and the radius as small as 4 nm, explaining their formation at high temperature and doping levels. Below 100 K, more strongly insulating behaviour is seen, suggesting that a charge-ordered state forms. The observed absence of charge density waves in this state is surprising within an excitonic insulator picture, but we show that it can be explained by the symmetries of the exciton wavefunction. Therefore, in addition to being a topological insulator, monolayer WTe2 exhibits strong correlations over a wide temperature range.Exciton condensation has been observed in various three-dimensional (3D) materials. Now, monolayer WTe2-a 2D topological insulator-also shows the phenomenon. Strong electronic interactions allow the excitons to form and condense at high temperature.