A Bloch point is a singular point around which the field vectors orient to nearly all directions. In magnetics, it naturally links classical and quantum magnetism and has not been observed directly so far. In ferroelectrics, it has only been predicted in several cases. Researchers from Institute of Metal Research, Chinese Academy of Sciences (IMR, CAS) and collaborators from Songshan Lake Materials Laboratory, Institute of Physics, Chinese Academy of Sciences (IOP, CAS), etc., directly observed polar Bloch points in strained ferroelectric films. This work was published in Nature Communications.
Based on their previous work about the polar meron lattice (Nature Materials 2020), they considered the model of a tensile-strained ultrathin ferroelectric PbTiO3 film sandwiched by symmetric electrodes in phase-field simulations and found the merons transform into Bloch points with the increase of the electrode thickness. Then, a trilayer SrRuO3/PbTiO3/SrRuO3 film was grown on the SmScO3 substrate by the pulsed laser deposition and the aberration-corrected scanning transmission electron microscopic imaging was used to observe the polarization configuration of polar Bloch points. Further phase-field simulations predicted that there exist a region of negative capacitance around each polar Bloch point.
The discovery of polar Bloch points enlarges the assembly of topological ferroelectric domain structures and implies novel applications in future integrated circuits and low power electronic devices.
The work was supported by National Natural Science Foundation of China, Guangdong Provincial Quantum Science Strategic Initiative, Youth Innovation Promotion Association CAS and Shenyang National Laboratory for Materials Science.
The transition from a meron to a Bloch point (left) and the atomic scale STEM image (right) (Image by IMR)
