Evidence for a monolayer excitonic insulator
Evidence for a monolayer excitonic insulator
复制标题
DOI：
10.1038/s41567-021-01422-w
复制
发表时间：
2021-12-23
期刊：
影响因子：
19.6
通讯作者：
Wu, Sanfeng
中科院分区：
文献类型：
--
作者：
Jia, Yanyu;Wang, Pengjie;Wu, Sanfeng
由于电子和空穴之间的配对而形成的绝缘状态已知存在于高磁场中的工程双层结构中。现在有证据表明，它们可以在零场的单层晶体中发生，拓扑和关联之间的相互作用可以产生各种量子相，其中许多仍有待探索。最近的进展已经确定单层WTe2作为一种有前途的材料，这样做在一个高度可调的方式。这种二维晶体的基态可以从量子自旋霍尔绝缘体静电调谐到超导体。然而，许多仍然未知的绝缘状态的间隙开放机制。在这里，我们报告的证据表明，量子自旋霍尔绝缘体也是激子绝缘体，所产生的自发形成的电子空穴束缚态，即激子。我们揭示了一个内在的绝缘状态的存在下，在干净的样品中的电荷中性点，并确认相关的性质，这种电荷中性绝缘体的隧穿光谱。我们提供的证据对替代方案的带状绝缘体或局部绝缘体，并支持存在的激子绝缘体相在清洁的限制。这些观察奠定了基础，了解一类新的相关绝缘体与非平凡的拓扑结构，并确定单层WTe2作为一个有前途的候选人探索量子相位的基态激子。
Insulating states that are formed because of pairing between electrons and holes are known to exist in engineered bilayer structures in high magnetic fields. Now evidence suggests they can occur in a monolayer crystal at zero field.The interplay between topology and correlations can generate a variety of quantum phases, many of which remain to be explored. Recent advances have identified monolayer WTe2 as a promising material for doing so in a highly tunable fashion. The ground state of this two-dimensional crystal can be electrostatically tuned from a quantum spin Hall insulator to a superconductor. However, much remains unknown about the gap-opening mechanism of the insulating state. Here we report evidence that the quantum spin Hall insulator is also an excitonic insulator, arising from the spontaneous formation of electron-hole bound states, namely excitons. We reveal the presence of an intrinsic insulating state at the charge neutrality point in clean samples and confirm the correlated nature of this charge-neutral insulator by tunnelling spectroscopy. We provide evidence against alternative scenarios of a band insulator or a localized insulator and support the existence of an excitonic insulator phase in the clean limit. These observations lay the foundation for understanding a new class of correlated insulators with nontrivial topology and identify monolayer WTe2 as a promising candidate for exploring quantum phases of ground-state excitons.