Fig. 4. Weak antilocalization of nodal-line fermions in SrAs₃.

a Back-scattering processes of nodal-line fermions on the poloidal plane of the torus-shaped Fermi surface in the momentum space (upper panel). The π Berry flux (yellow line) along the nodal-loop leads to weak antilocalization (WAL). The corresponding diffusion of nodal-fermions in the real space is two-dimensional (lower panel), which significantly enhances the quantum interference effect. b The low-field transverse magnetoconductivity Δσ(H)/σ(0), taken at T = 2 K and H⊥J, from eleven SrAs₃ crystals with different hole carrier densities (n_h) and the ratio (K₀/κ) between the radii of the nodal-loop (K₀) and the poloidal orbit (κ). c The transverse magnetoconductivity Δσ(H) for S1 together with the fits to the 2D WAL (red line) and 3D WAL (blue line) models. d Temperature-dependent phase coherence length l_ϕ for S1, following T⁻¹ dependence (blue dashed line) at high temperatures. The fit to the 2D WAL model is also shown (green solid line). e The excess conductivity Δσ_WAL as a function of σ₀ for various topological semimetals. The inset shows the Δσ_WAL of SrAs₃ crystals taken at 2 K with variation of the ratio K₀/κ.