- Accepted Paper
Nonsymmorphic time-reversal-doubled axion insulators
Phys. Rev. X - Accepted 21 September, 2026
DOI: https://doi.org/10.1103/jxlt-2slk
Phys. Rev. X - Accepted 21 September, 2026
DOI: https://doi.org/10.1103/jxlt-2slk
The axion insulator exhibits a topological magnetoelectric effect characterized by an axion angle , 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 (). In this phase, the partial axion angles () 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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