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A monolayer transition-metal dichalcogenide as a topological excitonic insulator.
Nature Nanotechnology ( IF 38.3 ) Pub Date : 2020-03-02 , DOI: 10.1038/s41565-020-0650-4
Daniele Varsano 1 , Maurizia Palummo 2 , Elisa Molinari 1, 3 , Massimo Rontani 1
Affiliation  

Monolayer transition-metal dichalcogenides in the T' phase could enable the realization of the quantum spin Hall effect1 at room temperature, because they exhibit a prominent spin-orbit gap between inverted bands in the bulk2,3. Here we show that the binding energy of electron-hole pairs excited through this gap is larger than the gap itself in the paradigmatic case of monolayer T' MoS2, which we investigate from first principles using many-body perturbation theory4. This paradoxical result hints at the instability of the T' phase in the presence of spontaneous generation of excitons, and we predict that it will give rise to a reconstructed 'excitonic insulator' ground state5-7. Importantly, we show that in this monolayer system, topological and excitonic order cooperatively enhance the bulk gap by breaking the crystal inversion symmetry, in contrast to the case of bilayers8-16 where the frustration between the two orders is relieved by breaking time reversal symmetry13,15,16. The excitonic topological insulator is distinct from the bare topological phase because it lifts the band spin degeneracy, which results in circular dichroism. A moderate biaxial strain applied to the system leads to two additional excitonic phases, different in their topological character but both ferroelectric17,18 as an effect of electron-electron interaction.

中文翻译:

单层过渡金属二卤化硅作为拓扑激子绝缘体。

T'相中的单层过渡金属二硫属化合物可以在室温下实现量子自旋霍尔效应1,因为它们在本体2,3的反向带之间表现出显着的自旋轨道间隙。在这里,我们证明了通过该间隙激发的电子-空穴对的结合能比在单层T'MoS2的典型情况下的间隙本身要大,这是我们使用多体扰动理论从第一原理开始研究的。这个自相矛盾的结果暗示了在自发产生激子的情况下T'相的不稳定性,并且我们预测它将产生重构的“激子绝缘子”基态5-7。重要的是,我们表明在此单层系统中,拓扑和激子顺序通过破坏晶体反转对称性来共同增加体隙,与双层8-16的情况相反,双层8-16通过打破时间反转对称性来减轻两个顺序之间的挫败感[13,15,16]。激子拓扑绝缘体不同于裸露的拓扑相,因为它提升了带自旋简并性,从而导致了圆二色性。施加在系统上的适度双轴应变会导致两个附加的激子相,它们的拓扑特征不同,但由于电子-电子相互作用,两者都是铁电的17,18。激子拓扑绝缘体不同于裸露的拓扑相,因为它提升了带自旋简并性,从而导致了圆二色性。施加在系统上的适度双轴应变会导致两个附加的激子相,它们的拓扑特征不同,但是由于电子-电子相互作用,两者都是铁电的17,18。激子拓扑绝缘体不同于裸露的拓扑相,因为它提升了带自旋简并性,从而导致了圆二色性。施加在系统上的适度双轴应变会导致两个附加的激子相,它们的拓扑特征不同,但是由于电子-电子相互作用,两者都是铁电的17,18。
更新日期:2020-03-02
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