With the increasing demand of new age electronics, there has been a constant attempt to incorporate the electronics with nanotechnology. This brings a dire need to include ferroelectrics in the electronics because of their intriguing functionalities. Upon reducing the dimension of ferroelectrics in nanoscale regime, owing to complex interaction between charge, strain, and chemical composition degrees of freedom, one can observe the presence of exotic topological structures associated with their dipole arrangement known as topological solitons (vortex structures, skyrmions, merons etc.).
One such solitons is the skyrmion: non-coplanar swirling field texture with polarization profile as small as 3 nm of size. Their small size and high sensitivity to external stimuli makes them quite suitable to be used for high density, low energy electronics. The creation and stabilization of polar skyrmions in thin film ferroelectrics is strongly driven by the strength of the depolarization field. Tuning of depolarisation field can be done by interface engineering of electrical and mechanical boundary conditions of ferroelectrics based heterostructure.One of the ways to achieve a fine balance between electrical and mechanical boundary conditions is by designing ferroelectric based heterostructures where each single crystalline ferroelectric film is intercalated by dielectric spacer material, viz. strontium titanate, SrTiO3 (STO) using sophisticated fabrication techniques like pulsed laser deposition.
My poster will demonstrate the role of boundary conditions in the formation of polar skyrmions in Bismuth ferrite based heterostructures. Bismuth ferrite (BFO) which is a type I multiferroic, exhibits multiple appealing properties like piezoelectric, domain-wall conduction, and optoelectronic responses etc on account of its robust ferroelectric and antiferromagnetic order parameters. The presence of skyrmions in the ferroelectric heterostructure is due to polarisation curling. In BFO this leads to distortion of associated oxygen octahedra and based on the Jahn-Teller effect, this is expected to yield new non-trivial energy levels (due to the t2g/eg band splitting) which can be exploited in effects like quantum tunnelling. The understanding of polar skyrmions in multiferroics can be significant in both, (1) exploring the fundamentals of spin-lattice coupling and (2) implementation in applications based on low energy electronics.
We will show how superlattice engineering in BFO/STO heterostructures opens way to maintain a delicate balance between the strain energy and electrostatic energy creating a suitable environment for skyrmion formation. Tuning thickness of each layer can also help understanding how different length scales influence the morphology and density of the skyrmions. Further characterisation is done by using techniques like x-ray diffraction, scanning probe microscopy and Transmission electron Microscopy. Probing further into the study of properties associated with these topological solitons can open possibilities to be engineered in various low energy electronics and transform the world of electronics industry.
About the presenter
Mahak Chhabra is a PhD candidate in CI Nagarajan Valanoor‘s group. My research focuses on correlated microscopy of solitons in Bismuth ferrite(BFO) based superlattice structures. Her work fits the FLEET Enabling Research Theme 1, Topological Materials.