Predicted monopole-antimonopole pair annihilation in an organic salt α-(BEDT-TTF)₂I₃ induced by linearly polarized light

Magnetic monopoles have not been observed yet since Dirac proposed a concept of them because the experimental observation needs to deal with extremely large energy of ~10¹⁶GeV. On the other hand, researchers have discovered that Dirac cones in band structures of materials can behave as sources (monopoles) or sinks (antimonopoles) of magnetic fields. Here we theoretically predicted that the monopole-antimonopole pair annihilation can occur in a photodriven α-(BEDT-TTF)₂I₃ which possesses slightly gapped Dirac cones in its band structure. We calculated quasienergies and Berry curvatures of nonequilibrium steady states in the driven α-(BEDT-TTF)₂I₃ under application of linearly polarized light by using the Floquet theory and found the pair annihilation of Dirac points accompanied by a phase transition from the Dirac semimetal to the normal insulator. This phenomenon can be realized at low energy of ~1eV. Therefore our results provide an opportunity to study the monopole-antimonopole pair annihilation in feasible experiments instead of the high-energy experiments.