Soft mode behavior in strained SrTiO3 thin film

We investigate the soft mode properties in strained SrTiO₃ thin films by employing the transverse-field Ising model, combining with the thermodynamic analysis to modify the strain dependent parameters. It is found that SrTiO₃ thin film shows the behavior of the quantum paraelectrics under the tensile strain smaller than the critical misfit strain ε_SC(T=0K) =0.038%. Under a strain slightly higher than ε_SC, the SrTiO₃ thin film shows the behavior of quantum ferroelectrics. Further increase of the tensile strain results in the greatly enhanced ferroelectricity in SrTiO₃ thin film.