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Studying peculiar properties of a long known metallic material researchers have chanced upon a new particle. It is related to the so-called Weyl fermions that the mathematician Hermann Weyl predicted almost ninety years ago. Weyl had overlooked the particle, which could have interesting applications in electronics.
When ETH professor Hermann Weyl arrived for his one-year tenure as guest professor at Princeton in the autumn of 1928, the quantum physicist Paul Dirac had just published his celebrated formula for the electron. That formula described the properties of so-called fermions, or quantum particles with half-integer spin, and its predictions - among them the existence of anti-matter – ushered in the era of modern particle physics. Weyl realized that, in principle, Dirac’s equation also allowed solutions for particles without mass. In 1929 he published a paper in which he described those massless particles with half-integer spin. They would later be called “Weyl fermions”.
Physicists at the ETH, together with researchers at Princeton University and at the Chinese Academy of Sciences, have now found a thus far unknown particle that their illustrious forebear had overlooked in his calculations and that had remained undetected for almost ninety years thereafter. They named it “type-2 Weyl fermion”.
Search for New Material Properties
The researchers hit upon the new kind of particle when trying to understand strange physical properties of the metal tungsten ditelluride (WTe2). “We were hoping to find especially so-called ‘topological’ properties that make certain quantum states more resistant to perturbations in this metal material”, explains Alexey Soluyanov, a researcher in the Computational Physics group at ETH Zurich.
In order to simulate the physical properties of the metal crystals the researchers ran calculations for 200,000 hours on supercomputers at the Swiss National Supercomputing Centre CSCS and at the Chinese Academy of Sciences. It required weeks of detailed derivations and calculations before the researchers came to the conclusion that they must have discovered something totally new: inside the tungsten ditelluride crystal there had to exist a thus far unknown type of fermion, the type-2 Weyl fermion.
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