A ferroelectric problem beyond the conventional scaling law

TL;DR

This paper reveals that size effects in ultrathin ferroelectric materials are intrinsic due to symmetry changes, invalidating the conventional scaling law and aiding the prediction of materials suitable for room-temperature ultrathin ferroelectric devices.

Contribution

It uncovers the intrinsic origin of size effects in ultrathin ferroelectrics through first-principles simulations, challenging the conventional scaling law.

Findings

Size effects are intrinsic, not extrinsic.

Electronic structure changes alter ferroelectric phase transition parameters.

The mechanism helps identify materials for room-temperature ultrathin ferroelectric devices.

Abstract

Ferroelectric (FE) size effects against the scaling law were reported recently in ultrathin group-IV monochalcogenides, and extrinsic effects (e.g. defects and lattice strains) were often resorted to. Via first-principles based finite-temperature ($T$) simulations, we reveal that these abnormalities are intrinsic to their unusual symmetry breaking from bulk to thin film. Changes of the electronic structures result in different order parameters characterizing the FE phase transition in bulk and in thin films, and invalidation of the scaling law. Beyond the scaling law $T_{\text{c}}$ limit, this mechanism can help predicting materials promising for room-$T$ ultrathin FE devices of broad interest.