• Accepted Paper

Nonsymmorphic time-reversal-doubled axion insulators

Yue Xie, Haohao Sheng, Quansheng Wu, Xi Dai, Zhong Fang, Hongming Weng, and Zhijun Wang

Phys. Rev. X - Accepted 21 September, 2026

DOI: https://doi.org/10.1103/jxlt-2slk

Abstract

The axion insulator exhibits a topological magnetoelectric effect characterized by an axion angle θ=π, while the time-reversal-doubled axion insulator (T-DAXI) can be viewed as two copies of an axion insulator related by time-reversal symmetry. In this work, we show that a nonsymmorphic topological crystalline insulator with glide (or screw) symmetry can host the nonsymmorphic T-DAXI phase, diagnosed by the nontrivial hourglass (screw) invariant δh=1 (δs=1). In this phase, the partial axion angles (θ±=π) are quantized by the glide or screw symmetry, and the gapped surfaces realize half-quantized quantum spin Hall states. Furthermore, we show that nonsymmorphic T-DAXIs also exhibit the spin-magnetoelectric effect. Namely, an external magnetic field can induce a topological nonlocal spin polarization in real space. When the magnetic field is time-periodic, this leads to an alternating spin current detectable in experiment. Using ab initio calculations, we demonstrate that mixed bismuth monohalides Bi4BrxI4−x realize the nonsymmorphic T-DAXI. Our findings not only reveal the symmetry-enforced T-DAXIs in nonsymmorphic topological crystalline insulators, but also demonstrate the spin-magnetoelectric effect as a detectable topological spin response in nonsymmorphic T-DAXIs.

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