Unusual Janus Bi₂TeSe₂ Topological Insulators Displaying Second-Harmonic Generation, Linear-in-Temperature...

Well-established knowledge about inversion-symmetric Bi₂TeSe_3- 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 Bi₃TeSe_3- topological insulators and open up opportunities for exploring hybrid nonlinear optoelectronic topological devices.