Layer-controlled growth of T_d-phase WTe₂ for enhanced nonlinear Hall effect and energy harvesting

Transition metal ditellurides with inversion symmetry breaking, particularly the T_d-phase of WTe₂, are of great interest due to their non-trivial topological band structures, Berry curvature, and the resulting nonlinear Hall effect (NLHE). Despite their significance, how intrinsic properties, such as layer number, influence the band topology and the NLHE remains experimentally unclear. In this work, we developed a layer-controlled growth technique for T_d-phase WTe₂ via chemical vapor deposition, where the moisture level was utilized to precisely tune the layer number. A proposed mechanism explains the moisture's role in the growth process. Experimentally, we observed that increasing the layer number from two to three layers leads to a pronounced enhancement of the NLHE, with the frequency of energy harvesting also showing layer dependence. These findings can be attributed to the increased Berry curvature with the number of layers, offering insights into the tunable topological properties and potential applications in energy harvesting technologies.