THz-induced polarization dynamics in Bi₄Ti₃O₁₂ thin film

Terahertz radiation and the effects induced by it can have great potential for practical application both for the development of new generation photonic and electronic devices and for fundamental research aimed at revealing new properties of well-known functional materials.¹ For ferroelectric materials, the advantage of using THz radiation lies in the possibility of an electrodeless application of an electric field to a ferroelectric and thus affecting its polarization in the pico(femto)second time range.

We discuss here conditions for polarization switching in Bi₄Ti₃O₁₂ 450nm-thick film on a BaSrTiO₃(4nm)/MgO substrate by a strong electric field of a picosecond terahertz (THz) pulse. Optical second harmonic generation used as a probe of polarization switching demonstrates hysteretic behavior in the whole range of electric field applied. However, numerical modeling of SHG intensity dependences on electric field using Landau-Khalatnikov equation shows the presence of a threshold THz field with an amplitude of E_th=5MV/cm . For modeling, exact values of Landau coefficients for the studied Bi₄Ti₃O₁₂ film were used2, the same for all dependences: the SHG hysteresis loops and power dependence. We found that for low fields EE_th, the polarization switches, and the SHG intensity increases sharply as a function of the THz power. At E_s=10MV/cm, the SHG intensity saturates. These results differ for conventional “low frequency” measurements where polarization switching is observed even with fields one order of magnitude lower.²

The work is supported by Russian Science Foundation, Grant No. 22-12-00334.

¹Jie Ji, et al, Sci. Rep. 8, 2682 (2018).

²V. M. Mukhortov, et al, Tech. Phys. 65, 118-123 (2020).