The state of matter above the critical point is terra incognita, and isloosely discussed as a physically homogeneous flowing state where nodifferences can be made between a liquid and a gas and where properties undergono marked or distinct changes with pressure and temperature. In particular, thestructure of supercritical state is currently viewed to be the same everywhereon the phase diagram, and to change only gradually and in a featureless waywhile moving along any temperature and pressure path above the critical point.Here, we demonstrate that this is not the case, but that there is awell-defined structural crossover instead. Evidenced by the qualitative changesof distribution functions of interatomic distances and angles, the crossoverdemarcates liquid-like and gas-like configurations and the presence ofmedium-range structural correlations. Importantly, the discovered structuralcrossover is closely related to both dynamic and thermodynamic crossoversoperating in the supercritical state, providing new unexpected fundamentalinterlinks between the supercritical structure, dynamics and thermodynamics.
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