Moiré Kramers-Weyl Fermions with Ideal Radial Spin Texture from Structural Chirality

We demonstrate that two-dimensional Kramers-Weyl fermions can be engineered in spin-orbit coupled twisted bilayers, where the chiral structure of these moiré systems breaks all mirror symmetries, confining Kramers-Weyl fermions to high-symmetry points in the Brillouin zone under time reversal symmetry. Our theoretical analysis reveals a symmetry-enforced, Weyl-like spinful interlayer moiré coupling that universally ensures an ideal radial spin-texture at arbitrary twist angles, under Cnz symmetry with n>2. First principles density functional calculation confirm the realization of these fermions in twisted α-In2Se3 homobilayers, where flat bands and out-of-plane ferroelectric polarization in each layer guarantee two-dimensional Kramers-Weyl physics with ideal radial spin textures.