The quantum paraelectric phase of SrTiO$_3$ from first principles

TL;DR

This paper uses first-principles calculations to explain how quantum fluctuations stabilize the paraelectric phase of SrTiO$_3$, accurately matching experimental observations of its soft mode and temperature-dependent properties.

Contribution

It introduces a microscopic ab initio approach that incorporates quantum fluctuations and mode coupling to accurately describe SrTiO$_3$'s quantum paraelectric state.

Findings

Quantum fluctuations stabilize the paraelectric phase.

Accurate prediction of ferroelectric soft mode frequency.

Effective modeling of temperature-dependent properties.

Abstract

We demonstrate how the quantum paraelectric ground state of SrTiO$_3$ can be accessed via a microscopic $ab~initio$ approach based on density functional theory. At low temperature the quantum fluctuations are strong enough to stabilize the paraelectric phase even though a classical description would predict a ferroelectric phase. We find that accounting for quantum fluctuations of the lattice and for the strong coupling between the ferroelectric soft mode and lattice elongation is necessary to achieve quantitative agreement with experimental frequency of the ferroelectric soft mode. The temperature dependent properties in SrTiO$_3$ are also well captured by the present microscopic framework.