Magnets are notoriously codependent. Try to break apart a magnet's north and south ends, and each half gets its own fresh set of two poles. Scientists have long hunted for a lone north or south pole—an individual particle carrying solely a positive or negative magnetic charge. Although such “magnetic monopoles” remain elusive, some have begun searching for virtual ones—clusters of electrons that behave like single magnetic charges.
Rather than searching for single particles, “we're using the creativity card that we have in condensed-matter physics ... to redefine new building blocks,” says Mete Atatüre, a physicist at the University of Cambridge. In a study published in Nature Materials, Atatüre and his colleagues have captured the first direct observation of magnetic monopoles that emerge naturally from the collective behavior of electrons. The researchers hope these objects could one day enable a more energy-efficient method for storing computer information.
Electrons in solid materials behave like tiny bar magnets; the strength and orientation of their magnetic fields are defined by a quantum property called spin, which acts like an atomic compass needle. Working in concert, the spins of many neighboring electrons can form particular patterns that appear as isolated regions of positive or negative magnetic charge. For the past 15 years scientists have been hunting for these monopolelike features emerging in various materials but had mustered only indirect evidence.
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In the new study, Atatüre and his team employed a new sensing technique that measures how tiny magnetic fields alter a single electron's spin at the fine tip of a diamond. They ran their detector over a freckle-sized sample of hematite, the primary component of rust, to map the texture of electron spins on its surface. While varying the sample's temperature, they were surprised to find that the spins spontaneously organized into whirlpool shapes that acted like magnetic monopoles—single positive or negative charges without partners.
“The measurements of these magnetic fields coming in and coming out, that's remarkable,” says Ludovic Jaubert, a theoretical physicist at University of Bordeaux who studies monopole features in other materials. “Once you can visually see these things, it's much easier to manipulate [them] to study further.”
These emergent features don't solve the enduring mystery of whether a magnet's poles can be fundamentally separated, but they may still prove valuable. Scientists have proposed that the pirouetting electron spins could be used to encode and transfer information in computers more efficiently than current methods, which typically rely on electrical charges that take more energy to move and sustain. Finally, spotting these quantum tornadoes is an important step toward building a new generation of electronics, Jaubert says. “It's really quite beautiful.”