Investigating THz light-driven ferroelectric transitions in Ca-doped SrTiO3

Titanate perovskites exhibit structural transitions characterized by the softening of phonon modes, typically leading to ferroelectricity below a critical temperature. However, in SrTiO3 (STO), these modes coexist with strong quantum fluctuations that suppress ferroelectricity, resulting in quantum paraelectric behavior. Recently, intense terahertz (THz) electric field excitation has been shown to dynamically induce a ferroelectric phase in the otherwise paraelectric STO. In this work, we investigate how this THz-induced transition is modified by Ca doping in STO. We find that significantly smaller THz fields are needed to induce ferroelectric behavior in the paraelectric phase of Ca-doped STO. We analyze this transition as a function of the THz field intensity, temperature, and doping to construct a phase diagram for the dynamical paraelectric-to-ferroelectric transition. Our results shed light on the intricate relationship between lattice dynamics, quantum effects, and THz excitation in STO-based perovskites, with potential applications for tuning ferroelectric properties at lower THz field.