Interview with António Costa: Where 2D Materials Meet Quantum Innovation

Since earning his PhD in 1998, António Costa—Associate in the Rossier Research Group—has dedicated his research to the theoretical exploration of low-dimensional magnetic systems, with a particular emphasis on spin excitations. By combining analytical approaches with computational modeling, he investigates how magnetic materials respond to external influences such as magnetic fields and electrical currents, uncovering fundamental mechanisms that underpin their behavior.

Your research focuses on 2D materials and the interface between plasmonics and magnonics. What recent breakthroughs stand out in your work?
On the magnonics side, we have been studying the spin excitations of a new kind of magnetic materials called altermagnets. These have properties that are sort of in-between ferromagnets and antiferromagnets. We have demonstrated that the lifetime of magnons in metallic altermagnets can be highly anisotropic, a property that can be exploited technologically to guide magnons along certain paths in the material. Further details can be found in the publication here.
On the magnonics/plasmonics interface, we have shown that graphene plasmons can couple strongly to the low-energy magnons in a 2D insulating ferromagnet, which can be uses as a new way to probe magnons in 2D materials, and also as a way to convert a magnetic into an electric signal and vice-versa. Magnons in 2D materials are difficult to probe with most existing techniques, because these require magnetic samples with large volumes. The 2D character of the graphene plasmon allows one to circumvent this requirement and potentially probe 2D magnons optically.

How do quantum mechanics and 2D magnetism intersect to shape future technologies like quantum computing or spintronics?
Magnetism is an intrinsically quantum phenomenon. Bulk magnetic systems, however, can usually be understood in terms of “semi-classical” magnetic moments; due to their huge number and large connectivity, classical statistical laws do a good job in describing most of their properties. 2D magnetism is special because the density of spins and their connectivity is drastically reduced (as compared to 3D), enhancing the role of quantum mechanics in determining their behavior. There is a hope that quantum 2D magnets can be tuned to reach highly correlated states that can be used as a resource for quantum computation. There is also the idea that some 2D systems with special properties can be used to manipulate coherently the electronic spin and provide means to perform quantum information transmission and processing efficiently.

How does combining fields like graphene and carbon nanotubes enhance the understanding of topological properties in 2D magnets?
One possibility is to use graphene to tune the properties of 2D magnets electrically, by proximity effect: the electronic structure of the magnet is affected by the electrons in graphene, which can be controlled externally by an applied voltage. Another possibility is what I mentioned above, the coupling between graphene plasmons and magnons in a 2D magnet. Carbon nanotubes may be used to encapsulate magnetic nanotubes, as demonstrated recently by the F. L. Deepak group (https://arxiv.org/abs/2405.14967, accepted for publication in Communications Chemistry). In that case it is expected that the magnetization of the encapsulated tube is oriented radially, which is very unusual and can affect the electrons in the carbon nanotube in weird ways.

What practical impacts could your work on magnetic materials and 2D systems have on energy or communication technologies?
The main goal of our work is to understand the fundamental aspects of low dimensional magnetic structures; so, application of our results certainly lies very far into the future. Nevertheless, understanding those fundamental aspects can be useful in choosing materials with specific properties, or in revealing new physical phenomena that can be used as a basis for new technologies. For instance, the interplay between charge and spin in 2D heterostructures can be useful for transduction of electrical into magnetic signals and vice-versa.

This is a technologically relevant problem for telecommunications devices. It is useful to remember that spintronics was born from fundamental research in the 1980’s and early 1990’s, and by the early 2000’s spintronic components were present in most commercial hard drives. So, doing fundamental research really pays off, even when we can’t quite see how right now.

Interview and Photography by Gina Palha, Communication, Conferences & Marketing Officer