  We investigate spin dynamics of artificial spin ice (ASI) where topological
defects confine magnon modes in Ni$_{81}$Fe$_{19}$ nanomagnets arranged on an
interconnected kagome lattice. Brillouin light scattering microscopy performed
on magnetically disordered states exhibit a series of magnon resonances which
depend on topological defect configurations detected by magnetic force
microscopy. Nanomagnets on a Dirac string and between a monopole-antimonopole
pair show pronounced modifications in magnon frequencies both in experiments
and simulations. Our work is key for the creation and annihilation of Dirac
strings via microwave assisted switching and reprogrammable magnonics based on
ASIs.

Mesoscale and Nanoscale Physics