  Dynamic axion insulators feature a time-dependent axion field that can be
induced by antiferromagnetic resonance. Here, we show that a Josephson junction
incorporating this dynamic axion insulator between two superconductors exhibits
a striking doubled Shapiro steps wherein all odd steps are completely
suppressed in the jointly presence of a DC bias and a static magnetic field.
The resistively shunted junction simulation confirms that these doubled Shapiro
steps originate from the distinctive axion electrodynamics driven by the
antiferromagnetic resonance, which thus not only furnishes a hallmark to
identify the dynamic axion insulator but also provides a method to evaluate its
mass term. Furthermore, the experimentally feasible differential conductance is
also determined. Our work holds significant importance in condensed matter
physics and materials science for understanding the dynamic axion insulator,
paving the way for its further exploration and applications.
