具有对称性的时间反演加倍轴子绝缘体
Nonsymmorphic Time-Reversal-Doubled Axion Insulators
AI总结：
研究揭示了非对称性拓扑晶体绝缘体中具有非对称性滑动或螺旋对称性的T-DAXI相，并展示了自旋磁电效应作为新的拓扑自旋响应。
摘要：
轴子绝缘体表现出由轴子角θ=π特征的拓扑磁电效应，而时间反演加倍轴子绝缘体（T-DAXI）可以视为通过时间反演对称性相关联的两个轴子绝缘体的副本。在本工作中，我们证明具有非对称性滑动或螺旋对称性的拓扑晶体绝缘体 hosting T-DAXI相。T-DAXI相的自旋解析拓扑性由某些自旋方向上的非对称性对称性不变量δ_g=1或δ_s=1保证。在该相中，部分轴子角被量化为π，且有间隙的表面实现了半量子自旋霍尔态。通过沿z方向施加外部磁场，电子在相反的(001)表面积累，产生实空间中的拓扑自旋极化。当磁场是时间周期性的，这导致可检测的交替自旋电流。使用从头计算，我们证明混合铋单卤化物Bi4Br3I和Bi4BrI3实现了非对称性T-DAXI，具有δ_g=δ_s=1。我们的发现不仅揭示了非对称性拓扑晶体绝缘体中对称性强制的T-DAXI，还引入了自旋磁电效应作为新的拓扑自旋响应。
英文摘要：
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 $δ_h=1$ ($δ_s=1$). In this phase, the partial axion angles ($θ^\pm=π$) are quantized by the glide and/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 Bi4Br3I and Bi4BrI3 realize the nonsymmorphic T-DAXIs. 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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