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arXiv · 2608.24989

Quantum spin Hall crystals at fractional filling of twisted MoTe$_2$

Xiaoyang Shen·Raul Perea-Causin·Christopher Ekman·Jiong-Hao Wang·Hui Liu·Emil J. Bergholtz
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Abstract

We predict and classify interaction-driven quantum spin Hall crystals (QSHCs), a class of states emerging at fractional filling through an interplay of topology and spontaneous translation-symmetry breaking. QSHCs form nearly degenerate manifolds whose members can realize distinct topological phases protected by time-reversal or valley $U(1)_v$ symmetry, with time-reversal acting nontrivially within the manifold. As a representative of this broad class of states we provide evidence for 9-fold quasi-degenerate $\sqrt{3}\times\sqrt{3}$ charge ordered QSHCs at $\nu = -8/3$ of twisted bilayer MoTe$_2$ near a $5^\circ$ twist. Here a $\mathbb{Z}_3$ index organizes states related by lattice translation into three time-reversal invariant states with nontrivial $\mathbb{Z}_2$ topology and three time-reversal related doublets whose individual members spontaneously break time-reversal and carry a $U(1)_v$ protected spin-Chern number. Finally, we determine the conditions that favor QSHCs over closely competing intervalley-coherent crystals.

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Xiaoyang Shen, Raul Perea-Causin, Christopher Ekman, Jiong-Hao Wang, Hui Liu, Emil J. Bergholtz. 2026-08-25. Quantum spin Hall crystals at fractional filling of twisted MoTe$_2$. https://arxiv.org/abs/2608.24989

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