The interaction-driven transition between quantum spin Hall and Mott insulators in the Bernevig, Hughes, and Zhang model is studied by dynamical cluster approximation, and found to be accompanied by the emergence of Green's function zeros already in the quantum spin Hall regime. The nontrivial interplay between Green's function poles and zeros leads to an exotic quantum spin Hall insulator exhibiting two chiral branches of edge Green's function poles and one of zeros. When symmetry breaking is allowed, a nontopological excitonic insulator is found to intrude between quantum spin Hall and Mott insulators. We find evidence that excitons in the Mott insulator, which become soft at the transition to the excitonic insulator, are actually bound states between valence and conduction bands of Green's function zeros, rather than between lower and upper Hubbard bands.

中文翻译：

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格林函数零点束缚态驱动的激子凝聚


通过动态簇近似研究了 Bernevig、Hughes 和 Zhang 模型中量子自旋霍尔和莫特绝缘体之间相互作用驱动的转变，发现伴随着量子自旋霍尔体系中已经出现的格林函数零点。格林函数极点和零点之间的重要相互作用导致一种奇特的量子自旋霍尔绝缘体，表现出边缘格林函数极点和一个零点的两个手性分支。当允许对称性破缺时，发现非拓扑激子绝缘体侵入量子自旋霍尔和莫特绝缘体之间。我们发现证据表明莫特绝缘体中的激子在过渡到激子绝缘体时变软，实际上是格林函数零点的价带和导带之间的束缚态，而不是下哈伯德带和上哈伯德带之间的束缚态。