Metallic electro-optic effects in topological chiral crystals

TL;DR

This study addresses metallic electro-optic effects in nonmagnetic SG198 topological chiral crystals, linking Berry curvature and orbital moment textures near multifold chiral nodes to observable optical responses. Using a combined tight-binding model and first-principles calculations across 37 SG198 materials, it demonstrates a nonzero Berry curvature dipole $D$ caused by energy offsets between opposite-chirality nodes and analyzes magnetoelectric EO effects governed by tensors $K$ and $G$. The work shows that BeAu supports magnetoelectric EO responses at experimentally accessible biases, with $E^{B}_{0_c}$ around $8\times10^{5}$ V/m and dominant $G$-driven onset, making it a practical platform for terahertz EO control. Overall, the results highlight new pathways for electrically tunable light–matter interactions in topological chiral metals and provide concrete material candidates for experimental exploration.

Abstract

Topological chiral crystals have emerged as a fertile material platform for investigating optical phenomena derived from the distinctive Fermi surface Berry curvature and orbital magnetic moment textures around multifold chiral band crossings pinned at the time-reversal invariant momenta. In this work, by means of tight-binding model and first principles based calculations, we investigate metallic electro-optic (EO) responses stemming from the Berry curvature and orbital magnetic moment of Bloch electrons across 37 materials belonging to space group 198 (SG198). Previously thought to vanish in SG198, our findings reveal a nonzero Berry curvature dipole attributed to the energetic misalignment between topologically charged point nodes of opposite chirality. Moreover, we find that the recently predicted magnetoelectric EO effects, which arise from the interplay between the Berry curvature and magnetic moment on the Fermi surface, are readily accessible in BeAu under experimentally feasible electric biases.

Figures (4)

• Figure 1: SG198 tight-binding model energy spectrum, Berry curvature, and orbital moment textures. a) Energy spectrum along high symmetry path of cubic Brillouin zone (BZ). Horizontal dashed lines indicate energies at which highfold degeneracies occur (red circles). b) Energy spectrum near fourfold (4f) fermion at $\Gamma$ with $C = -4$. $C = -1$ Kramers-Weyl point (KWP) appears $0.1eV$ below 4f fermion. c) Energy spectrum near sixfold (6f) fermion at $R$ with $C = +4$. d) Berry curvature and orbital moment textures of electron pockets near highfold nodes. Fermi surfaces correspond to topmost bands in b) and c) and are taken $30m$eV above each highfold node SM.
• Figure 2: Tight-binding model Berry curvature dipole (D), gyrotropic magnetic (K), and magnetoelectric EO (G) coefficients. a) $D$-resolved energy spectrum and energy dependent $D$, b) $K$-resolved energy spectrum and energy dependent $K$, c) $G$-resolved energy spectrum and energy dependent $G$. For these calculations, the temperature and damping term are assumed to be 300K and 25meV, respectively. Dashed black horizontal lines indicate energetic positions of highfold fermions at $\Gamma$ and $R$. Note: The color scale for each tensor type is chosen to highlight the sign of the contributions and not their magnitudes. For magnitude comparisons, please see Supplementary Materials SM.
• Figure 3: Structure of RhSi and energy dependent optical response tensors. a) Crystal structure of RhSi. b) $D$-resolved band structure and associated energy dependent $D$. c) $K$-resolved band structure and associated energy dependent $K$. d) $G$-resolved band structure and associated energy dependent $G$. For calculation details please see Supplementary Materials SM. Dashed blue and red horizontal lines indicate energetic positions of highfold fermions at $\Gamma$ and $R$, respectively. Note: The color scale for each tensor type is chosen to highlight the sign of the contributions and not their magnitudes. For magnitude comparisons, please see Supplementary Materials SM.
• Figure 4: Critical fields for EO response of SG198 materials. $E^B_{0_c} = \frac{1}{e}|\frac{K}{G}|$ measures the onset of the novel EO effects associated with $G$ whereas $E^E_{0_c} =\frac{\hbar ^2}{e}|\frac{V}{D}|$ does so for EO effects related to $D$. Fermi level $D$, $K$, $G$, and $V$ are used to calculate these critical fields SM.