Polar Order in Quantum Paraelectric SrTiO3-16 and SrTiO3-18 at Low Temperature

TL;DR

This study investigates polar order in SrTiO3-16 and SrTiO3-18 at low temperatures using SHG microscopy, revealing local polar regions without long-range order despite strong signals.

Contribution

It demonstrates that local polar regions exist in these quantum paraelectrics without forming a long-range ordered phase, using combined optical and diffraction techniques.

Findings

Weak and temperature-independent SHG in STO16 without electric field

Spontaneous SHG in STO18 below 36K

No structural change detected at low temperature

Abstract

Optical second-harmonic generation (SHG) in SrTi16O3 (STO16) and SrTi18O3 (STO18) was investigated using the SHG microscope. While no-biased STO16 exhibits weak and almost temperature-independent SHG signals, a marked SHG is observed under the electric field in the quantum paraelectric region. In STO18, strong SHG signals appear spontaneously below 36K. However, neutron and X-ray diffraction analyses indicate that no structural change appears at low temperature in STO18, and STO16 under the electric field. By taking into account the fact that the SHG is sensitive to the local polar-order, the combined studies reveals that the long-range order of polar phase does not develop on the both crystals and is frozen in local regions.