Dirac-Schwinger quantization for emergent magnetic monopoles?

In Refs. [1] , [2] , [3] , [4] Dirac and Schwinger showed the existence of a magnetic monopole required a charge quantization condition which we write following Dirac as e g 4 π ħ = n 2 , n = 0 , ± 1 , ± 2 , … . Here, g is the magnetic monopole charge and e is the electric charge of the positron. Recently, in Refs. [5] , [6] , it has been shown experimentally that frustrated spin-ice systems exhibit ‘emergent’ magnetic monopoles. We show that, within the experimental errors, the respective magnetic charges obey the Dirac-Schwinger quantization condition. Possible implications are discussed.