Fig. 6: Tunability of nodal line connectivity with strain.

a, b Splitting between the two bands crossing the Fermi level showing two different types of connectivity. In a the parameters of the tight-binding model are the ones obtained from fitting the model to the bands computed by DFT. On the other hand in b, to capture the effect of a lattice deformation, the out-of-plane hopping amplitudes are multiplied by a factor of 1/10, see Methods Sec. "Tight binding model" for details. The figures also show the mapping of the nodal lines onto the mirror plane torus (respectively viewed from an elevation of 30° and  −30°), where it is apparent that the configuration with the reduced out-of--plane hopping does not wind around the torus, and as such is in general not guaranteed to cross the Fermi level. On the other hand, the configuration with a stronger out-of-plane hopping fully winds twice around the torus, and is thus guaranteed to pierce the Fermi surface. Notice also that the nodal line winding along the meridian on the right-hand side of the torus corresponds to the KNL pinned along the high-symmetry path Γ − T.