Quantum paraelectricity and structural phase transitions of SrTiO₃ by on-the-fly machine-learned interatomic potentials

Strontium titanate (SrTiO₃) is a versatile building block for a variety of technologies and a ubiquitous playground for studying emergent phenomena in complex oxide materials and heterostructures. Central to many of its remarkable properties is the strongly anharmonic lattice dynamics, including competing ferroelectric and antiferrodistortive instabilities and the suppression of ferroelectricity by quantum fluctuations at low temperature. Here we employ machine-learned interatomic potentials trained on the fly [1] in combination with the stochastic self-consistent harmonic approximation (SSCHA) [2] to fully capture quantum and anharmonic effects and their temperature dependence, with the accuracy of the underlying first-principles description of the potential energy surface. We investigate the cubic to tetragonal transition characterized by the softening of the antiferrodistortive mode, and we further show that the anharmonic quantum fluctuations stabilize the paraelectric phase. This approach enables detailed studies of emergent properties in anharmonic materials including quantum paraelectrics.

[1] R. Jinnouchi, F. Karsai, and G. Kresse, Phys. Rev. B 100, 014105 (2019)

[2] L. Monacelli et al., J. Phys.: Condens. Matter 33, 363001 (2021)