i ct.qmat 25 Magnetische Monopole Magnetic monopoles ... sind Teilchen, über deren Existenz Paul Dirac 1931 spekulierte. Moessner war der Erste, der einen Stoff identifizierte, in dem sich magnetische Nord- und Südpole frei bewegen und beliebig weit voneinander entfernen können. Dies geschieht in Spineis – einer Familie von Substanzen, die durch eine besondere Kristallstruktur exotische Eigenschaften entwickeln. Hier sind die Monopole aber keine Elementarteilchen, sondern vielmehr Quasiteilchen, die sich als Ergebnis der Wechselwirkungen der Elektronen im Material bilden. Deren Existenz ist experimentell bestätigt worden. ... are particles whose existence was conjectured by Paul Dirac back in 1931. Moessner was the first scientist to identify a substance in which the magnetic north and south poles move freely and can be any distance apart. This occurs in spin ice – a family of substances that develop exotic properties due to their special crystal structure. Here, however, instead of elementary particles, the monopoles are quasiparticles formed as a result of interactions among electrons in the material. Their existence has been experimentally confirmed. The complicated physics of the underlying gauge theories can be illustrated by folding a piece of paper. “A generalization of spin liquidity is described mathematically by the same theory as folded paper,” Moessner explains. When making a paper airplane, a sheet of paper can only be folded neatly along a straight line. Trying to fold it along a curve would be impossible without creasing or even tearing it. “Similarly, there are particles that can’t move freely in three-dimensional space – they can only move in one direction,” says Moessner. “Working with researchers from Bangalore in India, we discovered that the fold tip – the point where the fold of a partly folded piece of paper ends – corresponds to an electric charge with a vector character. Rather than being simply positive or negative, it’s a charge with a direction.” Accordingly, its motion is constrained, for it can only move in the direction of its charge. “This is exactly what happens when you fold paper along a straight line. If you violate this restriction, it won’t do the paper any good.” Restricted motion also exists in higher-order spin liquids, which have been predicted theoretically and are now being sought experimentally. Emergence of mesoscale quantum phase transitions in a ferromagnet, Nature (2022). Unveiling the three-dimensional magnetic texture of skyrmion tubes, Nat. Nanotechnol. (2022). Metallic and deconfined quantum criticality in Dirac systems, Phys. Rev. Lett. (2022). Tunable chirality of noncentrosymmetric magnetic Weyl semimetals in rare-earth carbides, npj Quantum Mater. (2022). Weitere ausgewählte Highlights Further selected highlights Paper highlight Fractonic view of folding and tearing paper: elasticity of plates is dual to a gauge theory with vector charges, Phys. Rev. Lett. (2021).
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