Effect of Aspect Ratio of Ferroelectric Nanofilms on Polarization Vortex Stability under Uniaxial Tension or Compression

Mastering the variations in the stability of a polarization vortex is fundamental for the development of ferroelectric devices based on polarization vortex domain structures. Some phase field simulations were conducted on PbTiO3 nanofilms with an initial polarization vortex under uniaxial tension or compression to investigate the conditions of vortex instability and the effects of aspect ratio of nanofilms and temperature on them. The instability of a polarization vortex is strongly dependent on aspect ratio and temperature. The critical compressive stress increases with decreasing aspect ratio under the action of compressive stress. However, the critical tensile stress first decreases and then increases with decreasing aspect ratio, then continues to decrease. There are two inflection points in the curve. In addition, an elevated temperature makes both the critical tensile and compressive stresses decline, and will also cause the aspect ratio corresponding to the inflection point to decrease. These are very important for the design of promising nano-ferroelectric devices based on polarization vortices to improve their performance while maintaining storage density.

Highly Controllable Etchless Perovskite Microlasers Based on Bound States in the Continuum

Lead halide perovskites have been promising materials for lasing applications. Despite that a series of perovskite microlasers have been reported, their lasing modes are confined by either the as-grown morphology or the etched boundary. The first one is quite random and incompatible with integration, whereas the latter one strongly spoils the laser performances. Herein, we propose and experimentally demonstrate a robust and generic mechanism to realize well-controlled perovskite microlasers without the etching process. By patterning a one-dimensional polymer grating onto a perovskite film, we show that the symmetry-protected bound states in the continuum (BICs) can be formed in it. The intriguing properties of BICs including a widely spread mode profile and high Q factor, associated with the exceptional gain of perovskite, produce single-mode microlasers with high repeatability, controllability, directionality, and a polarization vortex. This mechanism can also be extended to two-dimensional nanostructures, enabling BIC lasers with different topological charges.