Researchers at ETH Zurich have made a groundbreaking discovery in ferromagnetism within a specially designed moiré material, challenging existing theories in the field. This new type of magnetism arises from the alignment of electron spins to minimize kinetic energy, shedding light on quantum mechanics and the nature of solid-state magnetism.
Magnetism in everyday objects, like a fridge magnet, depends on the uniform orientation of electron magnetic moments, a state that persists even without an external magnetic field. This phenomenon is due to the exchange interaction, a complex dynamic involving electrostatic repulsion among electrons and the quantum mechanical nature of electron spins, leading to magnetic moments. This is what renders materials like iron and nickel ferromagnetic, retaining their magnetic properties up to a certain temperature.
At ETH Zurich, a team led by Ataç Imamoğlu from the Institute for Quantum Electronics and Eugene Demler from the Institute for Theoretical Physics, has discovered an unconventional form of ferromagnetism in an artificially created material. Their findings have been published in the journal Nature.
The team developed a unique material by layering atomically thin sheets of two semiconductor materials, molybdenum diselenide and tungsten disulfide. The differing lattice constants of these materials create a two-dimensional periodic potential, which can be electron-filled through an applied electric voltage.
In this moiré material, electron spins are disorganized when each lattice site holds one electron. However, when electron numbers exceed lattice sites, allowing the formation of electron pairs known as doublons (indicated in red), the spins align ferromagnetically to reduce kinetic energy. This was demonstrated at ETH Zurich.
Imamoğlu notes the growing interest in moiré materials for studying quantum effects in strongly interacting electrons, though their magnetic properties were less understood. To explore these properties, his team analyzed the material’s response to varying electron fillings, determining whether it exhibited paramagnetic or ferromagnetic behavior by measuring light reflection for different polarizations.
Upon increasing the electron count in the material, they observed a sudden transition to ferromagnetic behavior, contradicting expectations from exchange interaction theories. Eugene Demler, with post-doc Ivan Morera, proposed this could be a realization of a mechanism predicted in 1966 by Yosuke Nagaoka, where aligned electron spins minimize kinetic energy, allowing doublons to quantum mechanically tunnel through the lattice.
Previously, such kinetic magnetism was observed only in model systems like coupled quantum dots and not in extended solid-state systems. Imamoğlu plans further studies to see if this ferromagnetism remains at higher temperatures. The material, for now, requires cooling to near absolute zero.
This study, titled “Kinetic magnetism in triangular moiré materials” by L. Ciorciaro, T. Smoleński, I. Morera, and others, was published on 15 November 2023 in Nature (DOI: 10.1038/s41586-023-06633-0).
Table of Contents
Frequently Asked Questions (FAQs) about Quantum Magnetism
What did the ETH Zurich researchers discover in their study?
The researchers at ETH Zurich discovered a new type of ferromagnetism in a custom-engineered moiré material. This new magnetism is based on the alignment of electron spins to minimize kinetic energy, providing new insights into quantum effects and solid-state magnetism.
How does this new type of magnetism differ from traditional ferromagnetism?
This new form of magnetism differs from traditional ferromagnetism as it does not rely solely on the exchange interaction, which is the standard mechanism for magnetic alignment in materials like iron and nickel. Instead, it involves a unique alignment of electron spins to minimize kinetic energy in a specially engineered moiré material.
What are moiré materials and why are they significant in this discovery?
Moiré materials are artificially created by layering two different semiconductor materials with differing lattice constants, resulting in a two-dimensional periodic potential. These materials are significant in this discovery as they allow for the investigation of quantum effects of strongly interacting electrons, particularly in understanding their magnetic properties.
What potential implications does this discovery have for the field of quantum physics?
This discovery has significant implications for the field of quantum physics as it challenges traditional theories of magnetism and provides a new understanding of the interaction between electron spins and kinetic energy. It opens new pathways for exploring quantum mechanics and could lead to advancements in magnetic materials and technologies.
What are the next steps for the researchers following this discovery?
The next steps for the researchers involve further experiments to determine if the observed ferromagnetism is preserved at higher temperatures. Currently, the material needs to be cooled to nearly absolute zero for the phenomenon to be observed, so understanding its behavior at higher temperatures is crucial for practical applications.
More about Quantum Magnetism
- ETH Zurich’s Novel Ferromagnetism Discovery
- Moiré Materials and Quantum Physics
- Understanding Quantum Magnetism
- Advancements in Solid-State Magnetism
4 comments
interesting read but kinda hard to grasp all the tech details.. what does this mean for everyday tech? like, could it change how we use magnets or something?
wow, this is some serious breakthrough stuff by ETH Zurich, who knew magnetism could get even more complicated? quantum physics is just mind-blowing.
gotta love how they’re always coming up with new stuff in science, moire materials? never heard of them before, but sounds super interesting!
ETH Zurich’s always at the forefront of cool discoveries, but I’m curious how this kinetic magnetism thing really works in practice. Need to dig deeper into this.