Well-established knowledge about inversion-symmetric Bi₂Te_xSe_3–x topological insulators characterizes the promising new-generation quantum device. Noticeably, the inversion asymmetric phase containing different surface electronic structures may create an extra topological phenomenon pointing to a new device paradigm. Herein, Janus Bi₂TeSe₂ single-crystal nanosheets with an unconventional stacking sequence of Se–Bi–Se–Bi–Te are realized via chemical vapor deposition growth, which is clarified by atomically resolved AC-STEM and elemental mapping. An obvious polarization-dependent second-harmonic generation with a representative 6-fold rotational symmetry is detected due to the broken out-of-plane mirror symmetry in this system. Low-temperature transport measurements display a strange metal-like linear-in-temperature resistivity. Anomalous conductance peaks under low magnetic fields induced by the weak antilocalization effect of topological surface states and the two-dimensional transport-dominated anisotropic magnetoresistance are revealed. These findings correlate the Janus Bi₂TeSe₂ phase with emerging physics topics, which would inspire fresh thoughts in well-developed Bi₃Te_xSe_3–x topological insulators and open up opportunities for exploring hybrid nonlinear optoelectronic topological devices.

中文翻译：

---

不寻常的 Janus Bi2TeSe2 拓扑绝缘体表现出二次谐波产生、线性温度电阻率和弱反局域化


关于反演对称 Bi ₂ Te _x Se _3–x 拓扑绝缘体的完善知识表征了有前途的新一代量子器件。值得注意的是，包含不同表面电子结构的反演不对称相可能会产生额外的拓扑现象，指向新的器件范式。在此，Janus Bi ₂ TeSe ₂ 单晶纳米片具有非常规的 Se-Bi-Se-Bi-Te 堆叠顺序，是通过化学气相沉积生长实现的，这由下式阐明：原子分辨 AC-STEM 和元素映射。由于该系统中平面镜对称性被破坏，检测到了明显的偏振相关二次谐波产生，具有代表性的六重旋转对称性。低温输运测量显示出奇怪的类金属线性温度电阻率。揭示了拓扑表面态弱反局域效应和二维输运主导的各向异性磁阻引起的低磁场下的反常电导峰。这些发现将 Janus Bi ₂ TeSe ₂ 相与新兴物理主题联系起来，这将激发对成熟 Bi ₃ Te _{x x} 拓扑绝缘体，为探索混合非线性光电拓扑器件提供了机会。