Giant Nonreciprocal Band Structure Effect in a Multiferroic Material

Multiferroic materials, combining ferroelectricity and ferromagnetism, can host complex band phenomena. Using density functional theory and symmetry analysis, we identify the multiferroic EuO as a prototypical system exhibiting a giant, switchable nonreciprocal band structure effect, that is an asymmetry in electronic bands at special points in the Brillouin zone, enabled by spin-orbit coupling. In particular, our results highlight the crucial role of magnetic symmetries - beyond inversion and time-reversal breaking. Ultimately, the predicted effect leads to a colossal bulk photovoltaic response, with injection currents far exceeding those in known oxides, enabling new cross-functionalities.