Strongly correlated excitonic insulator in atomic double layers
Strongly correlated excitonic insulator in atomic double layers
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DOI：
10.1038/s41586-021-03947-9
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发表时间：
2021-10-28
期刊：
影响因子：
64.8
通讯作者：
Shan, Jie
中科院分区：
文献类型：
--
作者：
Ma, Liguo;Nguyen, Phuong X.;Shan, Jie
激子绝缘体（ei）产生于半导体中束缚电子-空穴对（激子）（1,2）的形成，并为量子多玻色子物理提供了一个固态平台（3-8）。强激子-激子斥力有望通过抑制密度和相位波动来稳定凝聚的超流体和结晶相（8-11）。虽然已经报道了EI的光谱特征（6,12-14），但强相关EI状态的确凿证据仍然难以捉摸。在这里，我们证明了在过渡金属二硫化物（TMD）半导体双层中形成的强相关二维（2D） EI基态。当施加在两个电隔离的TMD层之间的偏置电压被调谐到一个填充束缚电子-空穴对而不是自由电子或空穴的范围时，就会产生准平衡的空间间接激子流体（15-17）。电容测量表明，流体是激子可压缩的，但电荷不可压缩，这是EI的直接热力学证据。该流体还与超过10的无量纲激子耦合常数密切相关。我们构建了一个激子相图，揭示了莫特跃迁和相互作用稳定的准凝聚。我们的实验为实现激子的奇异量子相(8)以及应用的多端激子电路铺平了道路（18-20）。到目前为止，只报道了激子绝缘体的特征，但这里提供了过渡金属二硫族半导体双层中强相关激子绝缘状态的直接热力学证据。
Excitonic insulators (EIs) arise from the formation of bound electron-hole pairs (excitons)(1,2) in semiconductors and provide a solid-state platform for quantum many-boson physics(3-8). Strong exciton-exciton repulsion is expected to stabilize condensed superfluid and crystalline phases by suppressing both density and phase fluctuations(8-11). Although spectroscopic signatures of EIs have been reported(6,12-14), conclusive evidence for strongly correlated EI states has remained elusive. Here we demonstrate a strongly correlated two-dimensional (2D) EI ground state formed in transition metal dichalcogenide (TMD) semiconductor double layers. A quasi-equilibrium spatially indirect exciton fluid is created when the bias voltage applied between the two electrically isolated TMD layers is tuned to a range that populates bound electron-hole pairs, but not free electrons or holes(15-17). Capacitance measurements show that the fluid is exciton-compressible but charge-incompressible-direct thermodynamic evidence of the EI. The fluid is also strongly correlated with a dimensionless exciton coupling constant exceeding 10. We construct an exciton phase diagram that reveals both the Mott transition and interaction-stabilized quasi-condensation. Our experiment paves the path for realizing exotic quantum phases of excitons(8), as well as multi-terminal exciton circuitry for applications(18-20).So far only signatures of excitonic insulators have been reported, but here direct thermodynamic evidence is provided for a strongly correlated excitonic insulating state in transition metal dichalcogenide semiconductor double layers.