Universal Features of Magnetic Behavior Originating from Linear Band Dispersion: α-BETS₂X and α′-BETS₂Y (BETS = Bis(ethylenedithio)tetraselenafulvalene, X = IBr₂, I₂Br, Y = IBr₂, ICl₂)

Unpaired electrons located at linear band dispersion (LBD) are exceptional and are called Dirac electrons (DE). They are given attention because of the unique electronic properties such as temperature (T)-independent resistivity, as if they belong to neither metallic nor nonmetallic substances. Meanwhile, universal features in magnetic behavior remain to be discovered. New organic DE systems, α-BETS2X and α′-BETS2Y (BETS = bis(ethylenedithio)tetraselenafulvalene, X = IBr2 and I2Br, Y = IBr2 and ICl2), were investigated using the X-ray single-crystal structural analyses, electrical resistivity and magnetic susceptibility (χ) measurements, and band structure calculations. They all exhibited an approximately linear T-dependence of χ, which was directly related to the LBD based on our proposed models. The findings will turn scientists' attention to the physical properties of organic DE at ambient temperature, as dynamics of DE have recently garnered increasing interest.