Nonlinear and Planar Hall Effects as Probes of Band Geometry in 1T‐TaS ₂ Driven by CDW Transition

Abstract The interplay between charge density wave (CDW) formation and electron correlations can lead to the emergence of novel topological phases in materials. In quasi‐2D 1T‐TaS 2 , below approximately 150 K, the system transitions from a nearly commensurate (NC) to a commensurate (C) CDW phase. Here, it is shown that the NC‐CDW to C‐CDW phase transition is marked by the emergence of a finite planar Hall and nonlinear Hall effect, alongside sign changes in the ordinary Hall and thermoelectric signals, indicating the reconstruction of the Fermi surface in the C‐CDW phase. The theoretical calculations suggest that the C‐CDW phase, stabilized by specific layer stacking, breaks both mirror and inversion symmetries. This leads to finite Berry curvature and a substantial Berry curvature dipole, giving rise to the observed planar Hall and nonlinear Hall effect. This study highlights the nontrivial band geometry‐driven physics of 1T‐TaS 2 and opens new possibilities for developing innovative sensors.