Evidence of the ferroelectric polarization in charge transport through WTe${}_2$ Weyl semimetal surface

We investigate electron transport along the surface of WTe${}_2$ three-dimensional single crystals, which are characterized by coexistence of Weyl semimetal conductivity and ferroelectricity at room temperature. We find that non-linear behavior of $dV\mathrm{/}dI(I)$ WTe${}_2$ differential resistance is accompanied by slow relaxation process, which appears as the $dV\mathrm{/}dI(I)$ dependence on the sign of the current change. This observation is confirmed by direct investigation of time-dependent relaxation curves. While strongly non-linear differential resistance should be expected for the zero-gap WTe${}_2$, the slow relaxation in transport is very unusual for well-conducting semimetals at room temperature. We establish, that non-monotonous dependence of the amplitude of the effect on driving current $\mathrm{\Delta }dV\mathrm{/}dI(I)$ well corresponds to the known Sawyer-Tower’s ferroelectric hysteresis loop. This conclusion is also confirmed by gate voltage dependencies, so our results can be understood as a direct demonstration of WTe${}_2$ ferroelectric polarization in charge transport experiment.