Fig. 1: Ferroelectric polarization and polarization induced nonreciprocal transport in WTe₂.

a Crystal structure of tetralayer WTe₂, with mirror plane \(M\) and the gliding plane \(G\) labeled by red dashed lines, respectively. The polar axis along z-axis is labeled by the red arrow. b Schematic illustration of a dual gate device structure. Gate voltages \({V}_{{{{\rm{t}}}}}\) and \({V}_{{{{\rm{b}}}}}\) can be independently applied to the top and bottom graphite, respectively. When applying both gate voltages along z direction, the vertical electrical field drives an interlayer sliding (shown as red arrow) through a mirror operation \(\widetilde{{M}_{{{{\rm{Z}}}}}}\) and realizes the switching of ferroelectricity as well as structural polarity. The figure is created partly with VESTA⁵⁸. c Schematic of the coupling between ferroelectric polarization and nonreciprocal transport. Under an applied in-plane magnetic field \(H\), the ferroelectric polarity of the system causes nonreciprocity that manifests as \({I}^{+}\ne {I}^{-}\), and this nonreciprocity can be reversed by reversing the ferroelectric polarity of the system. d The d.c. I–V characteristic of the rectification effect in WTe₂. The nonreciprocal transport in WTe₂ causes a rectification effect on current, reflected as a nonlinear IV curve, that switches sign when ferroelectricity is switched from P↑ to P↓. e Measurement schematic of nonreciprocal transport in noncentrosymmetric polar system, second harmonic voltage \({V}_{{{\mathrm{xx}}}}^{2{{{\rm{\omega }}}}}\) is probed while applying an a.c. current \({I}_{{{\mathrm{xx}}}}^{{{{\rm{\omega }}}}}\) along longitudinal x direction. Angle \(\theta\) and \(\varphi\) denotes the direction of magnetic field \(H\) with respect to the y- and z-axis, respectively.