Piezoelectric quantum spin Hall insulator VCClBr monolayer with pure out-of-plane piezoelectric response

Abstract

The combination of piezoelectricity with nontrivial topological insulating phase in two-dimensional (2D) systems, namely piezoelectric quantum spin Hall insulator (PQSHI), is intriguing for exploring novel topological states toward the development of high-speed and dissipationless electronic devices. In this work, we predict a PQSHI Janus monolayer VCClBr constructed from $\mathrm{VCC}{\mathrm{l}}_2$, which is dynamically, mechanically and thermally stable. In the absence of spin orbital coupling (SOC), VCClBr is a narrow gap semiconductor with gap value of 57 meV, which is different from Dirac semimetal $\mathrm{VCC}{\mathrm{l}}_2$. The gap of VCClBr is due to built-in electric field caused by asymmetrical upper and lower atomic layers, which is further confirmed by external-electric-field induced gap in $\mathrm{VCC}{\mathrm{l}}_2$. When including SOC, the gap of VCClBr is improved to 76 meV, which is larger than the thermal energy of room temperature (25 meV). The VCClBr is a 2D topological insulator (TI), which is confirmed by $Z_2$ topological invariant and nontrivial one-dimensional edge states. It is proved that the nontrivial topological properties of VCClBr are robust against strain (biaxial and uniaxial cases) and external electric field. Due to broken horizontal mirror symmetry, only out-of-plane piezoelectric response can be observed, when biaxial or uniaxial in-plane strain is applied. The predicted piezoelectric strain coefficients $d_{31}$ and $d_{32}$ are -0.425 pm/V and -0.219 pm/V, which are higher than or compared with ones of many 2D materials. Finally, another two Janus monolayer VCFBr and VCFCl (dynamically unstable) are constructed, and they are still PQSHIs. Moreover, their $d_{31}$ and $d_{32}$ are higher than ones of VCClBr, and the $d_{31}$ (absolute value) of VCFBr is larger than one.

10 pages, 12 figures

References in corpus (10)

• Quantum Spin Hall Insulator State in HgTe Quantum Wells
• Quantum Spin Hall Effect and Enhanced Magnetic Response by Spin-Orbit Coupling
• Computing topological invariants without inversion symmetry
• Large-Gap Quantum Spin Hall Insulator in single layer bismuth monobromide Bi${}_4$Br${}_4$
• Sign-reversible valley-dependent Berry phase effects in 2D valley-half-semiconductors
• Intrinsic piezoelectricity in monolayer $\mathrm{XS}{\mathrm{i}}_2{\mathrm{N}}_4$ (X=Ti, Zr, Hf, Cr, Mo and W)
• Colossal switchable photocurrents in topological Janus transition metal dichalcogenides
• Huge out-of-plane piezoelectric response in ferromagnetic monolayer NiClI
• Intrinsic piezoelectric ferromagnetism with large out-of-plane piezoelectric response in Janus monolayer $\mathrm{CrB}{\mathrm{r}}_{1.5}{\mathrm{I}}_{1.5}$
• Coexistence of intrinsic piezoelectricity, ferromagnetism and nontrivial band topology in Li-decorated Janus monolayer $\mathrm{F}{\mathrm{e}}_2\mathrm{SSe}$ with high Curie temperature

Cited by in corpus (2)

• Prediction of Magnetoelectric Multiferroic Janus Monolayers VOXY(X/Y = F, Cl, Br, or I, and X$\ne$Y) with in-plane ferroelectricity and out-of-plane piezoelectricity
• Tunable Topological Phase Transitions in a Piezoelectric Janus Monolayer