Simulating THz field-induced ferroeletricity in quantum paraeletric SrTiO₃ by solving Schrodinger-Langevin equation

Studies of light-matter interactions reveal that light can unravel the hidden properties of materials. For example, the higher critical temperature for superconductivity is observed by applying the light on K₃C₆₀. Also, light-induced topological phase transitions in ZrTe₅ and WTe₂ are experimentally demonstrated. Recent experiments reported that high intensity terahertz (THz) and near infreared field pulse can induce a ferroelectric transition in SrTiO₃ from its quantum paraeletric ground state [1-2]. Here, we investigate the THz field-induced transient ferroeletricity by solving the time-dependent lattice Schrödinger-Langevin equation. First, the description of quantum paraeletric SrTiO₃ based on the density functional theory calculation is investigated [3]. We found that the quantum description between ferroeletric soft mode and uniaxial lattice strain is essential to reproduce the experientially observed properties in quantum paraeletric SrTiO₃. Based on this study, we investigate the real-time dynamics of lattice wavefunction of ferroeletric soft mode in quantum paraeletric SrTiO₃ by solving time-dependent Schrödinger-Langevin equation [4]. We found that the THz field-induced transient ferroelecticity originates from the light-mixed state between ground and the first excited lattice wavefunctions of ferroeletric soft mode in quantum paraeletric SrTiO₃. In agreement with the experimental observations, our study reveals that the non-oscillatory second harmonic generation signal is main evidence of transient ferroeletricity in SrTiO₃. Our study unravels the microscopic mechanism of light-induced phase transition and provides the understanding of quantum paraeletric phase.