Nearly three-dimensional Dirac fermions in an organic crystalline material unveiled by electron spin resonance

Abstract

Materials containing Dirac fermions (DFs) have unique electronic properties, and have been extensively studied. Electron spin resonance revealed that α-ET₂I₃ (ET = bis(ethylenedithio)-tetrathiafulvalene) at 1 bar contained a nearly three-dimensional DFs above ∼100 K coexisting with standard fermions. The close charge-transfer ET–I₃ interactions account for temperature-sensitive three-dimensional (3D) band structures and temperature-independent resistivity behaviour. As 3D band structures cannot be depicted in a four-dimensional space, the analysis method proposed herein provides a general way to present important and easy-to-understand information of such band structures that cannot be obtained otherwise.