A new study led by Vinod M. Menon and his research group at The City College of New York shows that trapping light inside magnetic materials may dramatically enhance their intrinsic properties. Strong optical responses of magnets are important for the development of magnetic lasers and magneto-optical memory devices, as well as for emerging quantum transduction applications.

In their new article in the journal “Nature,” Menon and his team report the properties of a layered magnet that hosts strongly bound excitons — quasiparticles with particularly strong optical interactions. Because of that, the material is capable of trapping light — all by itself. As their experiments show, the optical responses of this material to magnetic phenomena are orders of magnitude stronger than those in typical magnets. “Since the light bounces back and forth inside the magnet, interactions are genuinely enhanced,” said Dr. Florian Dirnberger, the lead-author of the study.  “To give an example, when we apply an external magnetic field the near-infrared reflection of light is altered so much, the material basically changes its color. That’s a pretty strong magneto-optic response.”

“Ordinarily, light does not respond so strongly to magnetism,” said Menon. “This is why technological applications based on magneto-optic effects often require the implementation of sensitive optical detection schemes.”

On how the advances can benefit ordinary people, study co-author Jiamin Quan said: “Technological applications of magnetic materials today are mostly related to magneto-electric phenomena. Given such strong interactions between magnetism and light, we can now hope to one day create magnetic lasers and may reconsider old concepts of optically controlled magnetic memory.” Rezlind Bushati, a graduate student in the Menon group, also contributed to the experimental work.

The study conducted in close collaboration with Andrea Alù and his group at CUNY Advanced Science Research Center is the result of a major international collaboration. Experiments conducted at CCNY and ASRC were complemented by measurements taken at the University of Washington in the group of Prof. Xiaodong Xu by Dr. Geoffrey Diederich. Theoretical support was provided by Dr. Akashdeep Kamra and Prof. Francisco J. Garcia-Vidal from the Universidad Autónoma de Madrid and Dr. Matthias Florian from the University of Michigan. The materials were grown by Prof.  Zdenek Sofer and Kseniia Mosina at the UCT Prague and the project was further supported by Dr. Julian Klein at MIT. The work at CCNY was supported through the US Air Force Office of Scientific Research, the National Science Foundation (NSF) – Division of Materials Research, the NSF CREST IDEALS center, DARPA and the German Research Foundation.

https://www.nature.com/articles/s41586-023-06275-2

From The City College of New York’s Center for Discovery and Innovation and the Physics Department comes news of a new type of magnetic quasiparticle created by coupling light to a stack of ultrathin two-dimensional magnets. This achievement sprouting from a collaboration with the University of Texas at Austin lays the foundation for an emergent strategy to artificially design materials by ensuring their strong interaction with light.

"Implementing our approach with magnetic materials is a promising path towards efficient magneto-optical effects,” said CCNY physicist Vinod M. Menon, whose group led the study. “Achieving this goal can enable their use for applications in everyday devices like lasers, or for digital data storage.”

Dr. Florian Dirnberger, the lead author of the study, believes that their work exposed a largely unexplored realm of strong interactions between light and magnetic crystals. “Research in recent years brought forth a number of atomically flat magnets that are exceptionally well-suited to be studied by our approach,” he noted.

Looking ahead, the team plans to extend these investigations to understand the role of the quantum electrodynamical vacuum when quantum materials are placed into optical cavities. “Our work paves the way for the stabilization of novel quantum phases of matter that have no counterpart in thermodynamic equilibrium,” commented Edoardo Baldini, assistant professor at The University of Texas at Austin.

The development is reported in the current issue of “Nature Nanotechnology,” in a paper entitled “Spin-correlated exciton-polaritons in a van der Waals magnet.” 

The research was funded by the National Science Foundation, Army Research Office and the CREST-IDEALS Center at CCNY.

From a team of City College of New York physicists and their collaborators in Japan and Germany comes another advancement in the study of excitons — electrically neutral quasiparticles that exist in insulators, semi-conductors and some liquids. The researchers are announcing the creation of an “excitonic” wire, or one-dimensional channel for excitons. This in turn could result in innovative devices that could one day replace certain tasks that are now performed by standard transistor technology.

Florian Dirnberger, post-doc in Vinod Menon’s research group in CCNY’s Center for Discovery and Innovation, and one of the lead authors of the study that appears in the journal “Science Advances,” detailed the team’s breakthrough. “Our main achievement was to manage to create these excitonic wires, essentially one-dimensional channels for excitons, in what is otherwise a two-dimensional semiconductor,” he said. “Since charge neutral excitons are not simply controlled by external voltages, we had to rely on a different approach. By depositing the atomically thin 2D crystal on top of a microscopically small wire, a thousand times thinner than a human hair, we created a small, elongated dent in the two-dimensional material, slightly pulling apart the atoms in the two-dimensional crystal and inducing strain in the material. For excitons, this dent is much like a pipe for water and once trapped inside, they are bound to move along the pipe, realizing quasi one-dimensional transport of excitons.”

This advancement holds possibilities for new devices.

“Manipulating the motion of excitons at the nanoscale realizes an important step towards excitonic devices,” noted Dirnberger. “Platforms based on two-dimensional semiconductor transition-metal dichalcogenides offer an interesting new approach called straintronics.”

Possible outcomes include innovative devices based on excitons that operate at room temperature and could replace certain tasks performed by contemporary transistor technology.

In addition to Dirnberger and other members of Menon’s lab at CCNY, researchers led by Alexey Chernikov at Dresden University of Technology, and at the University of Regensburg (both Germany) participated in the study, along with researchers from Japan’s National Institute for Materials Science.