Dirac-Schwinger Quantization for Emergent Magnetic Monopoles?

In Refs.[1-4] Dirac and Schwinger showed the existence of a magnetic monopole required a charge quantization condition which we write following Dirac as $\frac{eg}{4\pi \mathrm{\hslash }}=\frac{n}{2},n=0,\pm 1,\pm 2,\dots$. 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.