In 2015, researchers Ma Xiuliang, Zhu Yinlian and Dr. Tang Yunlong of the Institute of Metal Research of the Chinese Academy of Sciences implemented strain regulation through the design of PbTiO3 / SrTiO3 ferroelectric multilayer films, and found that the flux fully closed domain structure in ferroelectric materials and successfully prepared Yushun Large-scale periodic arrays formed by alternating arrangement of clockwise and counterclockwise closed structures (Science 2015). After the publication of this work, it quickly aroused an upsurge in the international research on the new iron polarization topology and performance. On the basis of the above work, in 2016, the University of California Berkeley and Lawrence Berkeley National Laboratory prepared and used the same electron microscopy method to find iron in the PbTiO3 / SrTiO3 superlattice system with the same composition and different strain conditions Eddy domain array (Nature2016). At present, other possible new electrodeized topologies and their potential inducing new properties have become research hotspots in the field of low-dimensional oxide functional materials, and many relevant international research groups are carrying out all-round exploration and research on them.
During his visit to Berkeley from February 2017 to April 2019, Tang Yunlong, as one of the main experiment designers and completion staff, based on the aforementioned work, worked with the R. Ramesh research group of the University of California Berkeley and the professor of the University of California Berkeley L. Martin, Professor Chen Longqing of Penn State University, and Professor J. Junquera of the University of Cantabria in Spain and other research groups have cooperated in-depth and made another breakthrough in the study of the polarization topology of ferroelectric materials: they are in PbTiO3 / SrTiO3 superlattice The polarized lattice crystal lattices that are stable at room temperature are found in (Figure 1-2). On April 17, the relevant results were published online under the title of Observation of room-temperature polar skyrmions in the journal Nature.
Since 2009, the experimental observation of the magnetic lattice crystal lattice has set off a wave of related dynamics and theoretical physics research to explore its potential as a new spintronic device. If the corresponding lattice crystal lattice can be further discovered in the ferroelectric polarization system, this will undoubtedly be another major breakthrough in the research of ferroelectric polarization topology. Based on the in-depth exploration of various energy competition relationships in the PbTiO3 / SrTiO3 system, Tang Yunlong et al. Successfully prepared a series of PbTiO3 / SrTiO3 superlattice systems using SrTiO3 (001) substrates. Using aberration-corrected quantitative analysis methods of transmission electron microscopy and synchrotron radiation diffraction, intact skyrmion lattices were observed in [(SrTiO3) 16 / (PbTiO3) 16] 8 and other systems. The single stigmine is formed by large-scale agglomeration in the PbTiO3 layer, and there is a tendency to form a square lattice in the plane; there is a Néel-type dispersed or concentrated polarization component near the interface. The second principle and other theoretical calculations have measured that the skyrmion number is always +1.
This work revealed for the first time in real space the lattice lattice of the stigmine in the polarized system. Compared with the ferromagnetic system, this polarized stigmine crystal lattice can exist stably at room temperature and does not need to be induced by an external field. It is relatively easier to realize the follow-up kinetic behavior research and regulation. Electronic devices provide a way. At the same time, the experiment reveals that the electric dipole in the polarized system also has quasi-particle behavior similar to the special spin-condensation structure under certain conditions, which will undoubtedly open a new chapter for the study of the polarized topology and its performance relationship. On April 17th, Nature magazine titled "Electrifying skyrmion bubbles" during the same period, and highlighted the relevant results of the paper in the "NEWS AND VIEWS" section, pointing out its new leading role in condensed matter basic physics and potential applications.
Figure 1: (SrTiO3) 16 / (PbTiO3) 16 / (SrTiO3) 16 three-layer system and [(SrTiO3) 16 / (PbTiO3) 16] 8 superlattice low magnification cross-section dark field image and planar STEM imaging. The illustrations in c and d are the fast Fourier transform of the corresponding image. The three-layer structure contains band domains and a single sigma structure; the superlattice is mainly composed of a two-dimensional sigma structure.
Figure 2: [(SrTiO3) 16 / (PbTiO3) 16] 8 superlattice low-magnitude planar HAADF-STEM underfocus imaging of the lattice crystal lattice. This shows the 8-layer PbTiO3 in the planar TEM sample and the large-scale polarized lattice crystal lattice.
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