Photoinduced topological phase transition from a crossing-line nodal semimetal to a multiple-Weyl semimetal

We propose a simple scheme to construct a model whose Fermi surface is comprised of crossing-line nodes. The Hamiltonian consists of a normal hopping term and an additional term which is odd under the mirror reflection. The line nodes appear along the mirror-invariant planes, where each line node carries the quantized Berry magnetic flux. We explicitly construct a model with the $N$-fold rotational symmetry, where the $2N$ line nodes merge at the north and south poles. Photoirradiation induces a topological phase transition. When we apply photoirradiation along the $k_z$ axis, there emerge point nodes carrying the monopole charge $\pm N$ at these poles, while all the line nodes disappear. The resultant system describes anisotropic multiple-Weyl fermions.