A Dirac electron system in solids mimics relativistic quantum physics that is compatible with Maxwell’s equations, with which we anticipate unified electromagnetic responses. We find a large orbital diamagnetism only along the interplane direction and a nearly temperature-independent electrical conductivity of the order of $e^2/h$ per plane for the new 2D Dirac organic conductor, $\alpha \text{−}(\mathrm{BETS}{)}_2{I}_3$, where BETS is bis(ethylenedithio)tetraselenafulvalene. Unlike conventional electrons in solids whose nonrelativistic effects bifurcate electric and magnetic responses, the observed orbital diamagnetism scales with the electrical conductivity in a wide temperature range. This demonstrates that an electromagnetic duality that is valid only within the relativistic framework is revived in solids.

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• Aritcle URL : https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.027201
• RIKEN : https://www.riken.jp/en/