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   Domain-wall engineering and topological defects in ferroelectric and ferroelastic materials; Guennou, Mael  ; et alin Nature Reviews. Physics (2020), 2(11), 634-648 Ferroelectric and ferroelastic domain walls are 2D topological defects with thicknesses approaching the unit cell level. When this spatial confinement is combined with observations of emergent functional ... [more ▼] Ferroelectric and ferroelastic domain walls are 2D topological defects with thicknesses approaching the unit cell level. When this spatial confinement is combined with observations of emergent functional properties, such as polarity in non-polar systems or electrical conductivity in otherwise insulating materials, it becomes clear that domain walls represent new and exciting objects in matter. In this Review, we discuss the exotic polarization profiles that can arise at domain walls with multiple order parameters and the different mechanisms that lead to domain-wall polarity in non-polar ferroelastic materials. The emergence of energetically degenerate variants of the domain walls themselves suggests the existence of interesting quasi-1D topological defects within such walls. We also provide an overview of the general notions that have been postulated as fundamental mechanisms responsible for domain-wall conduction in ferroelectrics. We then discuss the prospect of combining domain walls with transition regions observed at phase boundaries, homo- and heterointerfaces, and other quasi-2D objects, enabling emergent properties beyond those available in today's topological systems. Ferroelectric and ferroelastic domain walls are 2D topological defects with thicknesses approaching the unit cell level and emergent functional properties. This Review discusses the exotic polarization profiles that arise at domain walls and the fundamental mechanisms responsible for domain-wall conduction. [less ▲] Detailed reference viewed: 114 (3 UL)Control of surface potential at polar domain walls in a nonpolar oxide; Guennou, Mael ; Kreisel, Jens et alin Physical Review Materials (2017), 1(7), Ferroic domain walls could play an important role in microelectronics given their nanometric size and often distinct functional properties. Until now, devices and device concepts were mostly based on ... [more ▼] Ferroic domain walls could play an important role in microelectronics given their nanometric size and often distinct functional properties. Until now, devices and device concepts were mostly based on mobile domain walls in ferromagnetic and ferroelectric materials. A less explored path is to make use of polar domain walls in nonpolar ferroelastic materials. Indeed, while the polar character of ferroelastic domain walls has been demonstrated, polarization control has been elusive. Here, we report evidence for the electrostatic signature of the domain-wall polarization in nonpolar calcium titanate (CaTiO3). Macroscopic mechanical resonances excited by an ac electric field are observed as a signature of a piezoelectric response caused by polar walls. On the microscopic scale, the polarization in domain walls modifies the local surface potential of the sample. Through imaging of surface potential variations, we show that the potential at the domain wall can be controlled by electron injection. This could enable devices based on nondestructive information readout of surface potential. [less ▲] Detailed reference viewed: 107 (4 UL) |
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