Two-Dimensional Metals for Piezoelectriclike Devices Based on Berry-Curvature Dipole

Piezotronics is an emerging field, which exploits strain to control the transport properties in condensed matters. At present, piezotronics research majorly focuses on insulators with tunable electric dipole by strain. Metals are excluded in this type of application due to the absence of the electric dipole. The recently discovered Berry-curvature dipole can exist in metals, consequently introduces the possibility of the piezoelectric phenomena in them. In this paper, we predict that strain can switch the Berry-curvature dipole, and lead to the nonlinear Hall effect in the two-dimensional (2D) 1H-MX2 (M = Nb, Ta; X = S, Se). Based on symmetry analysis and first-principles calculations, we show these 2D monolayer metals have the desired piezoelectriclike property: without strain, the Berry-curvature dipole is eliminated by symmetry, prohibiting the nonlinear Hall effect; while uniaxial strain can effectively reduce the symmetry to introduce sizable Berry-curvature dipole, and it can generate observable Hall voltage under a reasonable experimental condition. Due to the nonlinear and topological properties, the piezoelectriclike property here is quite different from the traditional one based on the electric dipole. Compared with the traditional piezoelectric materials, which can only exist in insulators, we manifest that the 2D metallic 1H-MX2 (M = Nb, Ta; X = S, Se) can be applied in the platform for piezoelectriclike devices such as strain sensors, terahertz detections, energy harvesters etc.