Ferroelectrically Controlled Chirality Switching of Weyl Quasiparticles

Abstract

Weyl quasiparticles, as gapless low-energy excitations with nontrivial chirality, have garnered extensive interest in recent years. However, archieving effective and reversible control over their chirality (topological charge) remains a major challeng due to topological protection. In this work, we propose a ferroelectric mechanism to switch the chirality of Weyl phonons, where the reversal of ferroelectric polarization is intrinsically coupled to a simultaneous reversal of the chirality of Weyl points. This enables electric-field-driven control over the topological properties of phonon excitations. Through a comprehensive symmetry analysis of polar space groups, we identify 27 groups capable of hosting symmetry-protected Weyl phonons with chiral charges $C = 1$, $2$, and $3$, whose chirality can be reversed via polarization switching. The first-principles calculations are performed to screen feasible material candidates for each type of chirality, yielding a set of prototypical ferroelectric compounds that realize the proposed mechanism. As a representative example, K$_2$ZnBr$_4$ hosts the minimal configuration of two pairs of Weyl phonons. Upon polarization reversal, the chirality of all Weyl points is inverted, accompanied by a reversal of associated topological features such as Berry curvature and surface arcs. These findings provide a viable pathway for dynamic, electrical control of topological band crossings and open new avenues for chirality-based phononic applications.

Figures (5)

• Figure 1: Schematic of ferroelectric switchable chirality of Weyl points. (a) denotes two ferroelectric structures connected by inversion symmetry, with opposite electric polarizations $\mathbf{P}$. (b) represents the Weyl points in these structures, respectively, with opposite chiralities.
• Figure 2: (a) Structures of K$_{2}$ZnBr$_{4}$ in the FE1 state, (b) in the PE state, and (c) in the FE2 state. (d) and (e) show the calculated ferroelectric switching pathway and corresponding polarization in K$_{2}$ZnBr$_{4}$.
• Figure 3: (a)-(c) respectively show the calculated phonon spectrum, the bulk and surface BZs, and the distribution of Berry curvature in the $k_{x}=\pi$ for K$_{2}$ZnBr$_{4}$ in FE1 state. Similarly, (d)-(f) correspond to the same properties of K$_{2}$ZnBr$_{4}$ in the FE2 state. The phonon branches forming the Weyl points are highlighted by blue curves.
• Figure 4: (a) and (d) show the (100) surface BZ of K$_{2}$ZnBr$_{4}$ for FE1 and FE2 states, with $\overline{W}_{i=1,2,3,4}$ indicating projected Weyl points. (b) and (e) show the projected spectra on the (001) surface for the FE1 and FE2 states, with red dashed circles indicating the closed loops. (c) and (f) present the corresponding surface energy dispersion along these loops.
• Figure 5: Schematic diagram of the NPHE under the temperature gradient, where $E$ represents the applied external electric field. The black arrows indicate the deflection of the nonlinear thermal current.