Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.
Phys Rev Lett. 2014 Mar 28;112(12):127601. doi: 10.1103/PhysRevLett.112.127601. Epub 2014 Mar 26.
All known proper ferroelectrics are unable to polarize normal to a surface or interface if the resulting depolarization field is unscreened, but there is no fundamental principle that enforces this behavior. In this work, we introduce hyperferroelectrics, a new class of proper ferroelectrics which polarize even when the depolarization field is unscreened, this condition being equivalent to instability of a longitudinal optic mode in addition to the transverse-optic-mode instability characteristic of proper ferroelectrics. We use first-principles calculations to show that several recently discovered hexagonal ferroelectric semiconductors have this property, and we examine its consequences both in the bulk and in a superlattice geometry.
所有已知的本征铁电体，如果去极化场未被屏蔽，其极化方向都无法垂直于表面或界面，但这并非是强制性的基本原则。在这项工作中，我们引入了超铁电体，这是一类新的本征铁电体，即使去极化场未被屏蔽，它们也可以极化，这种情况除了本征铁电体的横向光学模式不稳定性之外，还相当于纵向光学模式的不稳定性。我们使用第一性原理计算表明，最近发现的几种六方铁电半导体具有这种特性，并且我们在体材料和超晶格结构中都研究了其后果。
