Researchers at PSI have investigated a novel crystalline material that exhibits electronic properties that have never been seen before. It is a crystal of aluminum and platinum atoms arranged in a special way. In the symmetrically repeating unit cells of this crystal, individual atoms were offset from each other in such a way that they—as connected in the mind's eye—followed the shape of a spiral staircase. This resulted in novel properties of electronic behaviour for the crystal as a whole, including so-called Rarita-Schwinger fermions in its interior and very long and quadruple topological Fermi arcs on its surface. The researchers have now published their results in the journal Nature Physics.
They report a new kind of quasiparticle. Quasiparticles are states in material that behave in a certain way like actual elementary particles. Two physicists, William Rarita and Julian Schwinger, first predicted this type of quasiparticle in 1941, which came to be known as Rarita-Schwinger fermions. These have now been detected experimentally for the first time, thanks in part to measurements at the Swiss Synchrotron Light Source SLS at PSI.
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