Exceptional hexagonal warping effect in multi-Weyl semimetals

Hexagonal warping (HW) in three-dimensional topological insulators is, by now, well known. We show that non-Hermitian (NH) loss/gain can generate an exceptional HW effect in double Weyl semimetals (DWSMs). This unique feature of DWSMs has distinctive effects on Fermi surface topology. Importantly, in the presence of such a k3 spin orbit coupling mimicking term, the symmetry associated with the DWSMs is changed, leading to four exceptional points, among which two are degenerate. Introducing a driving field removes this degeneracy. The combined action of the NH warping and driving parameters leads to notable effects, including merging and tuning of exceptional points. We analyze the topological nature of the generated exceptional contours by evaluating several topological invariants, such as winding number, vorticity, and NH Berry curvature. We hope that our theoretical results will initiate possible experiments exploring NH HW effects.