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. When we apply photoirradiation along the k(z) axis, there emerge point nodes carrying the monopole charge +/- N at these poles, while all the line nodes disappear. In this model, photoirradiation induces a topological phase transition from a crossing-line nodal semimetal to a multiple-Weyl semimetal, where the surface state turns from a drumhead state into a Fermi-arc state.