Topological nodal line semimetals

Fang Chen^{1, †,}, Weng Hongming^{1, 2, ‡,}, Dai Xi^{1, 2}, Fang Zhong^{1, 2}

(a) By tuning m from positive to negative in Eq. (16), the nodal line with ζ₂ = 0 is fully gapped; (b) by tuning m from positive to negative in Eq. (17), the nodal line with ζ₂ = 1 first shrinks to a point, then grows into a line again.^[28]