Ultrahigh energy storage density in epitaxial AlN/ScN superlattices

Dielectric and antiferroelectric materials are particularly promising for high-power energy storage applications. However, relatively low energy density greatly hinders their usage in storage technologies. Here, we report first-principles-based calculations predicting that epitaxial and initially nonpolar AlN/ScN superlattices can achieve an ultrahigh energy density of up to $200\phantom{\rule{0.28em}{0ex}}\mathrm{J}/{\mathrm{cm}}^{\text{3}}$, accompanied by an ideal efficiency of 100%. We also show that high energy density requires that the system be neither too close nor too far from a ferroelectric phase transition under zero electric field. A phenomenological model is further proposed to rationalize such striking features.