This illustration shows a magnetic material being exposed to two laser beams whose electric fields turn in opposite directions. The material scatters back the light. If there is a difference in the intensity of the scattered light from the two beams, the material is in a topological phase. Image: Jörg Harms, MPSD.Much recent research has focused on ‘topological’ materials –intriguing solids that fall outside the standard classification of insulators and conductors. While the bulk of a topological material is insulating, they are also characterized by electrically conducting channels that appear at their edges. The resulting so-called topological phases are expected to play an important role in the future development of spintronics and quantum computing.
But topological phases are not restricted to electronic systems, they can also occur in magnetic materials whose properties are described in terms of magnetic waves – or magnons. Nevertheless, even though scientists have established techniques for generating and detecting magnon currents, they have so far been unable to directly ascertain a magnon topological phase.
Now, a research team from Germany and the US has shown that the presence of these topological phases can be directly verified by simply measuring the light scattered from a magnetic material. They report their findings in a paper in Physical Review Letters.
Just like a sound wave travels through the air, a magnon can travel through a magnetic material by creating a disturbance in its magnetic order. That order can be imagined as a collection of spinning tops, all with the same rotation axis. The magnon travels through the material by slightly tipping the rotation axes of these spinning tops.
A topological magnon phase is associated with channels that can carry a current of magnons along the edges of a material. Researchers are hopeful that such edge channels can be utilized to carry information in future spintronics devices, analogous to the way electric currents are used to transmit signals in today’s electronic devices. But before such technologies can be realized, scientists need to find a way to determine whether a magnetic phase is topological or not.
The research team studied a class of 2D magnetic materials structurally similar to graphene and exposed them to laser light with either a right- or a left-handed polarization, where the laser’s electric field turns either clockwise or anticlockwise around the laser beam’s axis. The researchers then analyzed the light scattered off the 2D material and showed that if the scattered intensity is different for the two polarizations, the material is in a topological phase. Conversely, if there is no difference in the scattered light intensity, then the material is not in a topological phase. The properties of the scattered light thereby act as a clear indicator of topological phases in these magnetic materials.
According to lead author Emil Viñas Boström at the Max Planck Institute for the Structure and Dynamics of Matter in Germany, the technique is easy to deploy and can be extended to other quasiparticles. “Raman scattering is a standard experimental technique available in many labs, which is one of the strengths of this proposal. In addition, our results are quite general and apply equally well to other types of systems consisting of phonons, excitons or photons.”
In the long term, the researchers hope that magnons can be used to construct more sustainable technological devices with a much lower energy consumption. “Utilizing topological magnon currents could potentially reduce the energy consumption of future devices by a factor of about a 1000 compared to electronic devices – although there are plenty of issues to be resolved until we get to that point,” says Viñas Boström.
This story is adapted from material from the Max Planck Institute for the Structure and Dynamics of Matter, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.