Physicists have long speculated about the existence of a rare state of matter called a quantum spin liquid. In this state, magnetic particles refuse to settle into an orderly arrangement, even at absolute zero temperature. Instead, they stay in a constantly shifting, entangled state driven by the strange rules of quantum mechanics. This creates unusual properties that resemble fundamental interactions in the universe, such as the way light and matter behave. Despite its potential significance, proving the existence of quantum spin liquids through experiments has been notoriously difficult.

In a recent study published in Nature Physics, an international team of researchers, including experimental physicists from Switzerland and France and theoretical experts from Canada and the U.S., uncovered evidence of this mysterious quantum state in a material called pyrochlore cerium stannate. They combined cutting-edge experimental techniques, such as neutron scattering at ultra-low temperatures, with advanced theoretical analysis. By examining how neutrons interact magnetically with the electrons’ spins in pyrochlore, they detected collective spin excitations behaving like lightlike waves, supporting the presence of a quantum spin liquid.

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