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Chirality is a structural configuration that cannot be superimposed on its own mirror image. Because chirality applies to human hands, mirror images of chiral structures are commonly referred to as being either ‘left-handed’ or ‘right-handed’.
While chirality is typically used to refer to certain molecules, ions and even galaxies, new research published in Proceedings of the National Academy of Sciences has shown swirling patterns of electrons known as polar vortices also have chirality. The idea that patterns of electrons can be left-handed or right-handed opens up a Pandora’s Box of new possibilities, with new data storage methods being among the most promising. The discovery could also lead to new way to couple magnetic or optical devices, making for better electrical switching – the basis of computing.
Study author Elke Arenholz, a senior staff scientist at the Berkeley Lab in California, noted that her team’s discovery expands on the idea of chirality, which has been most commonly associated with molecules like DNA and glucose.
“Chirality hadn’t been seen before in this electric structure,” Arenholz said in a news release.
The research team noted that the ability to distinguish between left-handed and right-handed electron vortices also opens up possibilities for studying and manipulating these vortices.
Imagine that one could convert a right-handed form of a molecule to its left-handed form by applying an electric field, or artificially engineer a material with a particular chirality.
Ramamoorthy Ramesh, Co-Author
To make their discovery, the study team layered lead titanate (PbTiO3) and strontium titanate (SrTiO3) in an alternating pattern to create a structure known as a superlattice. Structures similar to the one used in the study have been analyzed in the past for tunable electrical qualities that make them promising candidates for highly-accurate sensors and other technical devices.
Neither lead titanate (PbTiO3) nor strontium titanate (SrTiO3) has chirality on its own, but when they were precisely layered, they created swirling electron vortex structures that showed a handedness. The team said they were able to detect the initial patterns of electrons by using a powerful electron microscope. A novel X-ray technique known as resonant soft X-ray diffraction was used to establish that the patterns did indeed have chirality.
Study author Padraic Shafer, a research scientist at the Berkeley Lab, performed the X-ray part of the research along with Arenholz. The two scientists were able to use soft X-ray diffraction to probe nanometer-scale details in the electronic structures and properties of the superlattice.
“The X-ray measurements had to be performed in extreme geometries that can’t be done by most experimental equipment,” Shafer said.
Using swirling X-rays known as circularly-polarized rays, the study team could examine both left-handed and right-handed vortices in their samples. The California team partnered with researchers at the University of Cantabria in Spain and other experts to create mathematical models of the vortices, which helped to analyze the study data.
“It took a lot of time to understand the results, and a lot of modeling and discussions,” Arenholz said.
The researcher said there are currently looking into chirality in other materials and combinations of materials.
“There is a wide class of materials that could be substituted,” Shafer said, “and there is the hope that the layers could be replaced with even higher functionality materials.”
An extension of this research could look into ways to manipulate chirality in various materials, possibly by using materials with electrically-changeable or magnetically-changeable properties.
“Since we know so much about magnetic structures,” Arenholz said, “we could think of using this well-known connection with magnetism to implement this newly discovered property into devices.”
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