Two-Dimensional Topological Insulator Al₂SbBi with a Double-Layer Honeycomb Structure with Large Spin Splitting and Piezoelectricity for Spintronic Devices

Two-dimensional materials provide an ideal platform for uncovering intriguing quantum phenomena and developing nanoscale devices of versatile applications. Recently, AlSb in the double-layer honeycomb (DLHC) structure was successfully synthesized exhibiting a semiconducting nature [ ACS Nano 15, 8184 (2021)], which corroborates the preceding theoretical prediction and stimulates the exploration of robust DLHC materials. In this work, we propose a Janus DLHC monolayer Al 2 SbBi, the dynamical, thermal, and mechanical stabilities of which are confirmed by first-principles calculations. Monolayer Al 2 SbBi is found to be a quantum spin Hall insulator with a topological bandgap of about 0.2 eV, which presents large spin splitting and peculiar spin texture in the valence bands. Furthermore, due to the absence of inversion symmetry, monolayer Al 2 SbBi exhibits piezoelectricity and the piezoelectric strain coefficients d 11 and d 31 are calculated to be 7.97 and 0.33 pm/V, respectively, which are comparable to and even larger than those of many piezoelectric materials, for example, MoS 2 ( d 11 = 3.8 pm/V) and InSe ( d 11 = 1.98 pm/V) monolayers. Our study suggests that monolayer Al 2 SbBi has potential applications in spintronic and piezoelectric devices.