Transforming a strain-stabilized ferroelectric into an intrinsic polar metal with light

We explore the effects of chemical doping and photodoping in the strain-induced multiferroic EuTiO₃ grown on DyScO₃ substrates. The polar order is probed experimentally using second harmonic generation (SHG) and modeled using ab initio calculations. At low photodoping concentrations, we observe a reduction in SHG signal, indicating a destructive coupling between charge carriers and polar order in accordance with our simulations and expectations for a second-order Jahn-Teller driven ferroelectric. However, under increased photodoping the reduction in SHG plateaus at 84% of its original magnitude, indicating resilience of the polar order in the presence of a high concentration of delocalized electrons. This behavior stands in contrast with our first-principles simulations, indicating that EuTiO₃ undergoes a transition from ferroelectric to polar metallic character under photodoping. We suggest several hypotheses for the mechanism behind this change in distortion character.