Researchers at MIT have discovered a new state of matter with a new kind of magnetism. This new state, called a quantum spin liquid (QSL), could lead to significant advances in data storage. QSLs also exhibit a quantum phenomenon called long-range entanglement, which could lead to new types of communications systems, and more.
Generally, when we talk about magnetism’s role in the realm of technology, there are just two types: Ferromagnetism and antiferromagnetism. Ferromagnetism has been known about for centuries, and is the underlying force behind your compass’s spinning needle or the permanent bar magnets you played with at school. In ferromagnets, the spin (i.e. charge) of every electron is aligned in the same direction, causing two distinct poles. In antiferromagnets, neighboring electrons point in the opposite direction, causing the object to have zero net magnetism (pictured below). In combination with ferromagnets, antiferromagnets are used to create spin valves: the magnetic sensors used in
hard drive heads.
In the case of quantum spin liquids, the material is a solid crystal — but the internal magnetic state is constantly in flux. The magnetic orientations of the electrons (their magnetic moment) fluctuate as they interact with other nearby electrons. “But there is a strong interaction between them, and due to quantum effects, they don’t lock in place,” says Young Lee, senior author of
the research. It is these strong interactions that apparently allow for long-range quantum entanglement.
The existence of QSLs has been theorized since 1987, but until now no one has succeeded in actually finding one. In MIT’s case, the researchers spent 10 months growing a tiny sliver of herbertsmithite (pictured above) — a material that was suspected to be a QSL, but which had never been properly investigated. (Bonus points if you can guess who herbertsmithite is named after.) Using neutron scattering — firing a beam of neutrons at a material to analyze its structure — the researchers found that the herbertsmithite was indeed a QSL.
Moving forward, Lee says that the discovery of QSLs could lead to advances in data storage (new forms of magnetic storage) and communications (long-range entanglement). Lee also seems to think that QSLs could lead us towards higher-temperature superconductors — i.e. materials that superconduct under relatively normal conditions, rather than -200C.
Really, though, the most exciting thing about quantum spin liquids is that they’re completely new, and thus we ultimately have no idea how they might eventually affect our world. “We have to get a more comprehensive understanding of the big picture,” Lee says. “There is no theory that describes everything that we’re seeing.”
Research paper:
doi:10.1038/nature11659 – “Fractionalized excitations in the spin-liquid state of a kagome-lattice antiferromagnet”
